Hi, I guess you checked the radius arm bushings, so check the shocks, make sure they are not "sticky/stuck" ,this can happen if they get bad or bent, check rotors and see that the calipers are releasing and make sure there is not a "chunk" missing. You would not believe some of the things I have seen happen to trucks. You have checked your ball joints and tie rods tires and wheels.This is a 2-wheel drive? Check the steering box, make sure it is solid as well as pitman arm is good shape. If I can think of some thing else I will add in with it. It is hard to say with out looking at it first hand.