The chains and studded tires wear ruts in the road, and going into or out of the ruts can throw you around pretty hard.
He puts added shims in to cant the axle forward, something like 2 deg left and 3 deg right. Net result is the truck still goes down the road straight even with the ruts, and when you make a turn if you 'release' the steering wheel it just snaps back to dead straight. The service folks at your local dealer may know all about it, but if not call Buddy and discuss it with him. It is an easy job with big results and you get a fresh alignment out it.
Have fun
Terry