Take your truck in somewhere to get an alignment. If there are any worn parts, including ball joints, centerlink, tie rods, bushings, idler arm, etc., they will tell you what the problem is. They won't be able to align it until EVERYTHING is working right, so they will tell you what all is wrong, and you're under no obligation to have them fix it for you. Just say, "thanks," and go home and repair what's broken.