What everybody else said plus, one way to pin point the problem is to get a laser thermometer, take it for a drive untill everything is heated up and look for temp differences at each hub.
If one side of front or rear is much hotter than the other, thats where to look for a brake dragging.
Look not only for temp difference, but also for temp drop between the two sides over time.
Get a reading off of everything, rims brake lines calipers front of drum back of drum with the brake set etc..
Try to find a good 4x4 offroad speciality shop that also does alignments. If you dont have one around that does, contact them anyway and see who they recommend.
I would also see if you have any local 4x4 clubs. Even if you arent into offroading, car club folks will usually go above and beyond to help.
Keep in mind, the kid at the tire store looks at your truck and has no friggen idea how to deal with it.
They average "alignment tech" at most shops has about 3 days of training and just graduated from oil changing.
Good luck,