04 Explorer, poor straight line handling

[blue83ranger]

I just got an alignment done on my truck, an '04 explorer sport trac 4x4, as it was handling very badly. It would wander back and forth and be pretty unstable. The alignment was off and it is noticeably better but it still handles poorly. I wasn't able to personally take it in so I was able to talk to the guy that did it but I noticed a note he put on his checklist. It says "Increased steering effort when turning right, powersteering imbalance may lead to irregular vehicle pulls." I've searched, and there seems to be quite a few people describing the handling the same way to what I'm experiencing and a lot of people say it was a bad rear wheel bearing. I checked mine for looseness and they seem to be good. Does anyone have any suggestion on what the problem could be? I should also note I use to have 31 inch mud tires on it that were not balanced the best and the steering wheel would slightly shake back and forth. The alignment was done with a different set of rims and tires that are balanced correctly.