Mods for Gasser Towing Economy?

gearheadE30 said:

@Curtis - all of the warmup modifiers, from the factory, are out by 155-165F depending on the table. That was one of the first things I checked, and logging confirms it never falls back into warmup. If I'm not in warmup, is there still benefit to running higher thermostat temperatures? I had always heard there was for carbureted/TBI stuff, but once you get into dry manifolds and port injection, that the evaporation impact didn't matter so much, but that's all secondhand "knowledge" or worse.

One way to find out.  My next step would be to stab in a factory stat and watch injector pulsewidth after entering closed loop... all the way from 160 up to 205F and see how much it changes.  It's probably less than an all-iron LT1, but I promise that pulsewidth will get shorter as the incoming air continues to get hotter.  Less air and the O2 closed loop injects less fuel.  The ECM isn't modifying it, physics is. 

Much of what makes a "cold air intake" help is two things:  Keeps the intake air colder which allows for the ECM to add fuel (power) and removes restriction.  Adding a cold air intake would likely help you make more power with cooler air and thereby need less right foot to maintain the same speed, (probably a wash) but it won't do much (I'm told) for removing restriction, and therefore might not help you much.  A lot of these trucks have massive filter elements and big boxes that don't restrict much.  I was itching to do a CAI on my Express van until I pulled out the filter.  Dear god you could probably feed three 5.3L engines with that thing.

The big killer I'm told is that factory muffler.  Not only is it huge, but it makes the exhaust flow the whole way down, back forward, and down again.  I ditched mine for a Magnaflow.  Sounds great, but check the intarwebs for drone feedback and always take it with a grain of salt.  The Magnaflow I put on, every Express van owner said "no, no drone, it's quiet inside."  They all lied because they were embarrassed they spent that much money on a premium muffler only to ruin their driving experience.  I'll be adding some change to try and shut mine up.

I have the same engine in a 30,000 pound 38' rv pulling a towd.  I get that same mileage whether I'm going uphill, downhill, against the wind, with the wind.  

My suggestion is to get a bigger heavier trailer so you can justify the tow vehicle.    LOL

The airfoil idea is interesting, reminds me of the school bus spoilers. I didn't realize that these were actually for keeping the back of the bus cleaner: https://seeiiairfoils.com/school-buses/

Thermostat added to the rockauto list next time I have a decent size order together. With all the vehicles, I'm sure it won't be long...

My IATs stay pretty reasonable and the foam to the fender pickup is still more or less okay, but I discovered that GM actually made a different version of the same form factor airbox for the LLY and maybe some late LM7 diesel trucks. Same filter and upper section, but the inlet to the filter is dramatically bigger. GM must have seen some value in it to bother releasing a new part just for that truck. There was one on Ebay for $20 so I'm going to give that a try. I honestly don't expect anything, but it's cheap and easy.

Buy a bigger truck, need a bigger trailer...I've heard that one before that's exactly how this started. I was towing a small enclosed with a Tahoe before.

Towing slower works in the flat, good for maybe half an mpg which is meaningful. In the mountains/hills it is somewhere between a wash and worse on mileage - the engine speed is low enough at 65 mph that it has to kick down. If I hit the bottom of the hill at 75, I can let it lug back to 65 without shifting, get over the top, and coast down the other side. The same approach kind of doesn't work at lower speed because the speed drops so much that it just isn't practical. but yes, point taken - going slower is generally the cheapest and easiest option by far.

Someone cut open a stock 8.1 muffler, it's pretty restrictive but also no surprise that it works as well as it does for sound attenuation. Apparently the 6.0 muffler is the same, minus the resonance chamber at the end. I do want to get a backpressure measurement just for curiosity, but I expect I'll be changing the exhaust around a bit.

https://www.performancetrucks.net/forums/gm-engine-exhaust-performance-21/come-see-whats-inside-stock-nbs-dual-inlet-outlet-muffler-495831/page2/

The rabbit hole did lead me to one useful place: end of injection timing. My replacement cam has some overlap to it, where the stock cam has none. Stock, the EOIT is set up to always complete fueling before the intake valve opens, so that the heat of the valve can vaporize the fuel. With my cam, there is enough overlap that whatever fuel is puddled on the valve immediately gets sucked out the exhaust. I didn't really understand what was happening at first, but I knew I had a lot more moisture in the exhaust than I used to, along with a raw fuel smell. Several hours of reading later, I've got a pile of scribbles in a notepad and I think a decent understanding of what's up, so I did some testing of a few different EOIT settings with LTFT disabled so I could see what STFT was doing at different speeds and loads. If the trim was adding fuel for a given point, I was not combusting effectively. If it was pulling fuel, then more of the fuel being injected was actually being combusted, which is more efficient.

Result: stock isn't horrible. Advancing EOIT to match the additional advance vs. the stock cam was a marginal improvement, a few percent in terms of trims generally below 2000 rpm and 50% load. Advancing past that was notably worse, not just in how much of the fuel was being burned but also somewhat surprisingly in throttle response. It got pretty soggy, to the point where a 40 degree advance over stock meant as much as 500 additional rpm before shifting because I had to use more throttle for the same acceleration.

Going the opposite direction means some of the injection event is during an open intake valve. I did a few steps here, and I may need to do more that are even more extreme, but initial findings are that delaying injection proportional to the cam overlap change made nearly no difference versus stock. I suspect that my fuel injected during IVO was short circuiting out the exhaust just like fuel injected before IVO was doing with a more advanced value. A few more steps showed progressive improvement the more I retarded EOIT. I'm now at a value that, based on injector pulse width, means I inject all fuel up to the injector PW seen at highway cruise loads after the exhaust valve has closed, based on the cam card numbers. At higher load, of course there will be more overlap with EVO as pulse widths increase, so I expect the impact to be reduced at higher loads and higher engine speeds.

The results are surprising. Torque for a given throttle position at light load is up dramatically. I need to peruse the logs more, but it was immediately noticeable because the shift points for normal acceleration dropped several hundred rpm because I wasn't using as much pedal. The fuel economy for my work commute exceeded all expectations. It very consistently is right at 10.8 mpg for my half hour drive, no matter what I changed. Today's commute: 11.9 mpg. that's the best city/suburban cycle mileage this has ever gotten. Hopefully it's not a fluke. fuel trims back this up, so I guess I may need to retune the maps a bit if it ends up being consistent. Will be interesting to see what it gets on the highway now.

I doubt there will be much difference towing because the injector pulse width is so much longer and puddling probably matters less, but I'll keep my fingers crossed. Either way, it's still interesting and rewarding to see the result, and the throttle response improvement alone makes it all worthwhile.

codrus (Forum Supporter) said:

Keith Tanner said:

I know that we often see a small (1-2 mpg) increase in cruising efficiency when turbocharging Miatas, and I've always attributed that to basically eliminating any pumping losses in the intake. I don't know if that's legit or not, but you can look at the power increase as an efficiency increase. 

I'm curious if those numbers with stock ECUs or with aftermarket ones?

AIUI, the biggest pumping losses are through the mostly-closed throttle plate, and the biggest reason why small engines are usually more efficient than large ones is that with less displacement you have to open the throttle wider to make the same amount of cruising power.  Same reason why EGR improves fuel economy.

Stock ECU. Aftermarket ECUs tend to do better (especially on older Miatas) because they're more likely to be in closed loop at cruise. But I was quoting as close to an A-B as possible. At cruise, the only real difference is the addition of the turbo and associated plumbing. I could be wrong. 

Positive displacement supers tend to drop 1-2 mpg because you're always paying the price of spinning that blower, and the bypass is small. 

gearheadE30 said:

I know, I know - slow down. But let's ignore that one for a minute. 2004 Suburban 2500, 8.1, 4L85E. Still on narrow 245 tires, 3.73 gears. Stock everything except roller rockers, Raylar cam, and tune, because the stock cam and lifters failed. It gets 7.5-8 mpg towing my mini toy hauler trailer at 70-75 mph. I do let her lug back on the hills and generally am able to keep it locked up in 4th turning 2200-2300 rpm.

It's a great truck, but I tow a lot and even a small improvement makes a big difference. Specifically, would an intake and exhaust directionally help, or would they just give me more power with which to burn fuel and lug back less in the mountains? There's a lot of opportunity for power it seems, as I have ~10+ kpa drop vs. ambient pressure even at 3500 rpm and WOT on the intake side. I don't have any good WOT logs all the way out to 4800 revs yet, but that part of the range isn't so important to me. The exhaust is a similar story. I don't have any numbers, but it's a single 2.5" for an 8.1 liter engine, and it's actually even smaller than that inside the muffler. Cats are staying regardless., and keeping the stock manifolds. 

Online, everyone just looks at the dyno numbers, or has turbodiesel trucks where the rules are a little different. Intake is good for 25 horsepower, exhaust is good for closer to 40 from the results I've seen. Both have gains all the way down to my towing engine speed. Anyone have experience with reducing pumping losses to improve economy? Or is it just going to be a case of more air, so it can use more fuel? Mostly a thought exercise right now, but putting 20k+ miles a year on this thing, and being a long term keeper vehicle, it might be worth some effort. Also, like most of us, I can't leave well enough alone.

The beast in question:

Cold air improves power but at a cost of lower fuel mileage.  For best fuel mileage use warm air.   Lower exhaust back pressure  helps fuel mileage.  But may cause real droning noise.  Giving you a real headache. 
  Headers can slightly help but most headers aren't designed for the camshaft you'll use.  Plus a lot of "headers" are simply tubular exhaust manifolds. 
   In general Headers have a length and size based on the camshaft in use.  Plus all the tubes are exactly that length.  If you need to dimple the tubes to clear spark plugs or get access to the bolts.  You've lost any potential gain.  

Yeah, noise is a real concern. I have another system I built for my K1500 and is quiet; I'll probably try to mimic that. Currently you can't hear the exhaust at all on this thing, it's just intake and wind noise. Which honestly is relaxing.

I'm not likely to do headers on this one. The stock manifolds are actually pretty decent; there's been some dyno testing to prove them out.

I did install the diesel airbox. Bolts right in, factory part, same air filter. Fender opening resized to match, and new foam gasket applied. Interestingly, it is noticeably quieter than the original airbox bottom. I don't have a great explanation for that unless fresh foam gaskets really made that much difference. I haven't had a chance to log restriction yet, do any WOT pulls, or actually tow with it. I don't expect much from it, but for the money it will be interesting to put numbers to it.

Improved mileage is holding with the EOIT changes, Lots of city driving, but I'm still mid 11s which as good as I can hope for.

still need to do some WOT runs to see if the airbox made any restriction differences. It did not make a difference for loaded or unloaded economy as far as I can tell, but I continue to be surprised how much quieter the more open airbox is.

I did a ~500 mile trip towing with a stock temperature thermostat over the weekend. My average was about half an mpg worse than the last similar trip I took. That wouldn't be a lot if I was getting 25 mpg, but as a percentage, dropping from a bit above 8 mpg down to 7.4 mpg average is around 8% worse. Similar ambient conditions, similar terrain, but it was a bit warmer out this time. Logging showed it was pulling 1-2 degrees of timing climbing hills where it wasn't doing that with the lower temp stat. So that probably didn't help, but I think most of the difference was because the fan was spending a lot more time engaged. Every hill it would lock up, where this almost never happened unless it was hot out with the AC running on the 180F stat. Even if there was an efficiency improvement with the higher coolant temperature, the fan in particular appears to be more than offsetting it.

In reply to gearheadE30 :

Your MPG is likely the the same with and without the trailer.

When I had my 8.1L Burb, it would get 15 mpg on the highway, no trailer. Dropped a bit with a trailer of course.  The 4L85e tends to get better mileage than the Allison trans does, which isn't a surprise considering the size of the Allison. 

Richard Holdener did header tests on the 8.1L, stock manifolds vs 2 different sized full length headers. The difference was minimal on the stock engine, so headers probably are worth the expense in your case.

In reply to SV reX :

After reading the initial post and looking at the provided picture my mind went precisely the way yours did.  

We own a very large bumper pull camper that we pull with my Ram 2500 and it's a huge drop in economy when we tow.

I have reasoned that certainly the weight doesn't help, but that the ginormous flat front of that camper is truly the biggest obstacle to reasonable economy.  I further reasoned that one of those wings would be the right way to cut a smoother hole through the air.

unloaded MPG pre-cam on the highway was around 14 for me. Highest I ever saw was a 14.6 average on some county highways going a bit slower.

Now, I get about 12.5 on the interstate, or up to 13.5 on slower county highways. I also went to some more aggressive tires since a lot of the moto pits can get pretty muddy and I've gotten stuck in the past. I'm sure the tires didn't help either, and I somewhat regret that decision. They didn't look nearly so aggressive in the internet pictures...

The Richard Holdener 8.1 videos have been excellent. I was surprised how little a difference headers made on that engine, but I agree, not really a great place for me to spend my money. Replacing the intake would be more worthwhile, as would the cat back exhaust.

Long time ago. Four wheeler magazine did project MPG.  The article in multiple pages is here. 
 

http://performanceunlimited.com/projectmpg/about_mpg.html

Interesting, that looks like a lot of things similar to what I've been doing with mine. And their comments about cams generally hurting economy would appear to be very true in my case.

Just got back from a trip out to Wyoming towing my 6x12 enclosed trailer with a friend's F150 3.5 ecoboost with the 10 speed. We did this because we didn't need the burb's interior space on this trip, and we thought it would get a few mpg better economy.

End result: 9.9 mpg. I did this same trip with the same trailer and the suburban a while back, and got 9.8 mpg average. Same driver (me) going basically the same speed (70-75 mph) for around 3000 miles. So that was an interesting outcome we really weren't expecting. The Ford is a really nice truck though, and both the engine and transmission really impressed me. It delivered power surprisingly similarly to the big 8.1, happily pulling as long as it was above about 2000 rpm. We tried the various drive modes, manual mode lugging the engine, locking into 8th to stay out of boost a bit, etc, and none of it seemed to make a dramatic difference aside from tow haul mode hurting economy a bit because it's not really a big trailer and didn't need the higher shift points to pull it. by the end of the trip, we settled on locking out 10th gear to prevent hunting, using tow haul mode in the mountains for the automatic engine braking, and running in Eco mode once we got out into the flat stuff.

The suburban is averaging about 12.5 mpg in suburban mostly unladen use right now. Manageable, but still between 1 and 1.5 mpg worse than before the cam. Driving it with no trailer or hitch hauler down to texas in a bit, will get some long-distance unloaded data from that trip. I'm guessing 12.5 to 13 mpg since it's always been about the same at 75 mph as it is on the local suburban drive cycle. The only time it is notably better is country highways that are 55-65 mph and it will sneak up on 14 mpg.

How old is the trailer? And has it ever been serviced? My thought is that if it's got a lot of miles and hasn't been serviced, maybe some new bearings or hubs could reduce the rolling resistance? 
 

Its just a guess, but since you got similar mpg with the f150 and the suburban, it makes me thing it's a trailer thing. 
 

Also, fwiw, I went from Falken Wildpeak AT3 to Continental terrain contact a/t (more Highway focused) on my ram 1500 and noticed a 1-2 mpg increase on the highway. 

In reply to Hoppps :

Trailer is a 2009 or something like that, but I did bearings on it recently. 

Just drove the Burb unloaded to Texas and back....12.5 mpg is not great. 

I do have Vredstein Pinza ATs on it now, which are much more aggressive than what the internet pics would suggest. That's definitely not helping. 

I also discovered that my Burb is a California truck, which means 4 cats instead of 2. That's not helping things much. The additional Cali cats are long skinny ones with very little face area; I'm sure they do wonderful things for flow. 

gearheadE30 said:

Interesting, that looks like a lot of things similar to what I've been doing with mine. And their comments about cams generally hurting economy would appear to be very true in my case.

Just got back from a trip out to Wyoming towing my 6x12 enclosed trailer with a friend's F150 3.5 ecoboost with the 10 speed. We did this because we didn't need the burb's interior space on this trip, and we thought it would get a few mpg better economy.

End result: 9.9 mpg. I did this same trip with the same trailer and the suburban a while back, and got 9.8 mpg average. Same driver (me) going basically the same speed (70-75 mph) for around 3000 miles. So that was an interesting outcome we really weren't expecting. The Ford is a really nice truck though, and both the engine and transmission really impressed me. It delivered power surprisingly similarly to the big 8.1, happily pulling as long as it was above about 2000 rpm. We tried the various drive modes, manual mode lugging the engine, locking into 8th to stay out of boost a bit, etc, and none of it seemed to make a dramatic difference aside from tow haul mode hurting economy a bit because it's not really a big trailer and didn't need the higher shift points to pull it. by the end of the trip, we settled on locking out 10th gear to prevent hunting, using tow haul mode in the mountains for the automatic engine braking, and running in Eco mode once we got out into the flat stuff.

 

The suburban is averaging about 12.5 mpg in suburban mostly unladen use right now. Manageable, but still between 1 and 1.5 mpg worse than before the cam. Driving it with no trailer or hitch hauler down to texas in a bit, will get some long-distance unloaded data from that trip. I'm guessing 12.5 to 13 mpg since it's always been about the same at 75 mph as it is on the local suburban drive cycle. The only time it is notably better is country highways that are 55-65 mph and it will sneak up on 14 mpg.

My guess ( and it's only a guess ) is that trailer  may have dropped the transmission down a gear or two and it increased  the boost pressure just enough to need more fuel,   
   My 2016 Ford F150 ( regular cab) got 21.6 mpg going from Mpls to San Diego empty.  And 17.3 coming back pulling a U Haul car trailer and a 4664 pound car  plus well over a 1000 pounds of spares.  It only had a 6 speed and n the road it stayed in 6th gear. 
     Running to and from work I average 22.+ mpg ( empty )  unless I use E85 which drops the mileage down to  20 ish. 

This thread reminded me of a former co worker who had his commute go from 19miles round trip the 124 a day. (3 years from retirement ) .

He had a 'burb but I can't recall the year.  He asked myself and another hot rodder what can I do to get more than 10mg.? We suggested the normal hot rod stuff,Intake Headers,free flowing exhaust. The truck was fuel injected so the induction stayed the same,I actually modded is stock air box opening and made it 100% cold air inlet. He went with a K&N filter.

Put long tube headers on it with a full 2 1/2 exhaust.

new plugs and a canned tune "chip" he did spend about $1500.

When he told us he now getting 17mpg we felt pretty good about our hot rod skills. Lol

He still went to the gas station every 2 days but he was not on E went he got there. He said he could do 5 legs instead of 4 but was stopping for coffee anyway.

So with all this I wouldn't underestimate a set of long tube headers and good exhaust in you MPG quest.

Maybe look at Gale Banks packages,My buddy did one on his 454 powered motor home and took it from 7.5 to 9.5mpg. I think that thing is 40 ft long.

Richard Holdener is very good for sure,but sometimes the area under the curve and the improvement below the rpm the Dyno pull starts is impressive .

On the eco boost towing,speed/air load make a huge difference. It's all about how much boost your getting. I hated it but 65 MPH is 4 mpg better (on the lie o meter) than 70! 8.5/12.5. 80 mpg was 6.5!

In reply to Cyclone03 :

Thanks for the input, exhaust is potentially on the list but I'm still on the fence about headers for towing. It seems like everyone who puts them on an 8.1 truck ends up needing to replace plug wires regularly because even the heat shielded ones get cooked. I'm also still waffling on the muffler because noise + towing really sucks. But I did make one improvement that so far has been worth it: my 8.1 is a 50 state truck, meaning it has 4 catalysts. The precats are a 3" pipe with a cat substrate, where the main cats are 6+" diameter so that you still have good flow area. I found some references to these things being a real flow killer, so I now have a 49 state legal exhaust with just the 2 large diameter cats. I don't have a lot of miles on it yet, but average is about half an mpg better unloaded. I didn't expect any unloaded difference, but I am towing the trailer to California in a few weeks and that will be the real test. I can say that it made a dramatic seat of the pants difference - the exhaust change improved performance as much as swapping the cam did.

I guess this thread should really just be a build thread for that truck, because there's a couple other useful things to document:

• My AC was overcharged, and on the highway it would trip the high pressure switch at 450+ psi. Not good. Lots of compressor cycling, and high load. I fixed that problem, and now the compressor doesn't cycle and my economy with the AC on picked up half an mpg or so. It used to be ~1 mpg worse with the AC on, now it is only about half an mpg. I wasn't looking for economy here, I only looked into it because it seemed like the compressor cycling was abnormal and I was worried about killing the clutch.
• The Raylar/PRW roller rockers I installed have been removed. After 15,000 miles, I pulled the valve covers just to take a look and found that the roller tip was starting to deform the valve tips, and the valves were no longer rotating. I don't understand why this would happen, but with stock rockers reinstalled, the engine is MUCH quieter. No notable performance difference between stock and roller rockers, I have a very hard time believing the Raylar 18hp claim as I don't feel any difference, and 18 hp is a lot.

18hp from the same ratio as stock definitely seems a stretch. 

The injector timing you ended up with definitely seems counter intuitive. We usually optimize this on a dyno and it's definitely engine dependent, and rpm dependent. Haven't really fooled with it at part throttle, but the transport time in the port is definitely different under vac conditions vs wot (where most of your advice will be).  Nice testing.

2200 miles of testing later and I've got some halfway decent comparison numbers. Last time I did this trip, my average speed was very similar and I was on highway tires and got 7.6 mpg. This time, I'm on AT tires at got 8.4 mpg. The main differences are going back to the stock rockers and the 49-state exhaust mod, and I have to assume the exhaust made the biggest difference. The AT tires are the same size as the old HT tires, but they are pretty soft and I'm sure hurt economy at least a little. I did retune the VE table slightly after the exhaust change as LTFT was showing higher VE at higher load and higher rpm, which is what you'd expect for less restriction. 

Interesting sidebars from tuning-

• This engine is VERY sensitive to IAT. When it heat soaks, like stopping for fuel, it knocks a bit until IAT comes down. At some point I had flattened out the IAT ignition compensation because I was seeing it cut timing, and internet lore suggested this was an easy power bump. As it turns out, if you tune the ignition map properly, you do end up needing the fairly aggressive IAT compensation in place. 
• A lot of my data logs show that I'm in fuel trim cell 22 when I'm towing. Many cals use different settings, but in general there is a 4x4 grid of LTFT memory set up by engine speed vs. MAP. There are also several modes beyond these 16, for things like idle, warmup, WOT, etc. Some vehicles cover the whole VE table with one LTFT cell, but this truck does have subdivisions. FTC 22 is WOT/high load - even though my throttle position may only be 50-60 percent for a light grade or something, I am close enough to WOT MAP that it goes into this mode where LTFT locks to its max value and it uses purely STFT. It will never use a negative LTFT if all cells have a negative value, in that case it locks to 0. It shouldn't impact overall economy too much because STFT still should get back to stoich, but it did emphasize some inaccuracy in my VE tuning. After retuning for the exhaust, my LTFTs are a bit better than they were before, so when in FTC 22, LTFT is now 0 instead of being at 3-5. From logging this seems to have helped avoid rich spikes if I'm in and out of FTC 22. Does it help a lot? doubtful, but my nerd brain is happy seeing nice clean transitions in and out of all these modes. 

After all this fiddling, I think I finally have the calibration about as good as I can make it. I had an average speed (not moving average, total engine-on average) of 64 mph on this trip which is fairly aggressive, with this much frontal area 8.4 mpg doesn't seem too bad.

Headers v. Plug wires.

my friend uses porcelain like plug wire ends on his 454 swapped into an International pick up with headers,they are touching 3 tubes.

Towed ~5000 miles in the last 3 weeks.

Based on datalogs, the intake modification was good for between 1-2 kPa of restriction improvement which was very surprising to me. It's marginally louder under load. Overall, worth the effort for how little it cost.

49 state exhaust mod continues to show a big difference, which is good and bad. If I drive with my previous habits, which I did for most of the trip, it averaged almost exactly half an mpg better. It's not any louder somehow, and there's notably more grunt at low rpm. This is good because I can carry a lot more speed on hills in the mountains without resorting to a downshift. It's bad because more air means more fuel. The instantaneous economy gauge is interesting because what used to be 6-7 mpg minimum in 4th at highway speeds up hills can now dip into the 5 mpg range consistently before a downshift. 

There's just enough torque on tap now so that I can use cruise control and not have it hunt between 3rd and 4th any time there's a slight grade. This is good for relaxing. This burns dramatically more fuel than using my right foot. Using cruise over about 1000 miles of that trip completely killed the 0.5 mpg gain, and bumped my average speed up by 2 mph over that distance because it wasn't lugging back up the hills. 

I have very little drive time with no load since the exhaust mod, but in general it seems to only have made a difference at higher load (makes sense) so in daily driving, any improvement is small enough that it's lost in my measurement error. 

Low Rolling Resistance truck tires. Expensive but worth it

Still dragging stuff around with the Suburban. One thing I wanted to come back to here was that I never could figure out why the transmission shift points and converter lockup were inconsistent, and why sometimes it would hang on to 3rd instead of using 4th. 

It turns out that there is an "optimal timing" table that is used as part of the torque stabilization calculation. The PCM checks to make sure that there is enough torque in the next gear to try to prevent hunting, and if it doesn't think there is, it will delay the upshift. At least in my stock 2004 calibration, there's a big island of higher timing on this table. Other year cals I have for comparison don't have this, and optimal timing pretty much looks like stock high octane timing table plus a couple degrees. I used an optimal timing table out of an earlier vehicle and now it shifts where I expect it to, which has helped fuel economy a bit. Pretty easy to keep the revs down now, though obviously this didn't do anything for actual engine efficiency or maximum power.

I couldn't find anything useful online about the optimal timing table, so I figured it was worth a post here.

I also bought a new trailer. It's bigger and heavier as an 8.5*18 at 5100 lbs empty, but tows well and I think the rounded corners help aero quite a bit. I get about 8 mpg towing between 70 and 75 mph.