High Mileage ATF

So what makes ATF that is designated as "high mileage" different than regular ATF? More additives? Different additives?

Mostly more seal conditioners I think, Valvoline Maxlife ATF is some good stuff if that's what you're asking.

we use max life exclusively at work. its a different additive pack and more seal conditioners as mentioned. only issue we have heard from using it is it will cause the seals to swell slightly and switching back to a standard fluid later causes issues.

Actually I was looking at that in the full synthettic. I have a trans out at the moment to replace a flex plate. It only has 42k on it but I will be doing a service on it and replacing most of the fluid. I saw some of the fluids that ate for transmissions that have more than 75k and it got me thinking. The max life Castrol is what i was going to use as it I recommended for the car but I was curious about the others and what the difference was.

I also should have mentioned, always go with the full synthetic DEX VI spec fluid. It's thinner than Dex III and related, but the conventional fluids shear down to a similar viscosity very quickly, whereas the synthetic is shear stable.