Chevy Equinox LNJ / 3400 V6 problems

My brother has not had the ignition recall service done yet on his 2006 Chevrolet Equinox. It has been hard to start (takes several tries) for a while now, but lately it's also had trouble holding idle and starts stumbling/stuttering at times while driving. The CEL indicates a single thrown code: P0301, cylinder #1 missfire detected.

First instinct was to check the plugs, so we replaced all the plug wires and all plugs except #1, because it is nearly impossible to access. Now the engine idles fine, but under load it stumbles and bucks like it's about to throw a rod and has so little power that my brother can't even back the car up my (steep) driveway.

Next step is to disconnect the front engine mount and roll the engine forward to replace the #1 plug. But even if one cylinder was bad, wouldn't the other 5 produce enough power to at least drive it out of my driveway? If so, what should we check next--coil pack, ecu, maf, crank/cam sensors? ODB2 is still only reporting P0301. Do any of you guys know these GM V6 engines?

replace the plug, start with the easy stuff right?

Maybe not so easy, we think the plug may be cross threaded. We'll see in the morning.

I'm skeptical that one worn out plug would cause symptoms that severe

We tried but couldn't get the #1 plug out without damaging the head. Whoever put it in last did a bang up job.

The odb2 was throwing P0300 this morning, random multiple cylinder misfire. Local parts store had coil packs in stock so we replaced the ignition coil and the engine seems to run fine now.