Just to be sure its the wheel thats off center, jack up the front so you can steer it easy left to right. Go full left, count the turns to full right, split the count and you should have center of the gear box. You should also feel a slight drag across center, if not adjust the box. The tight spot on center keeps the truck going straighter and you from steering it so much.
http://chevy.oldcarmanualproject.com/booklets/5220mts01.htmJoe
