I think the trucks in question are stock & next to new. Mine is.
The rest of the time there is no "feedback" thru the steering wheel.
He said it was new. I suggested he contact GM directly. The comments about lifts/worn parts are the more normal causes. Not likely his problem.
Mark
If you don't think the dealer is doing enough, you should contact GM directly. It's whats known as Death Wobble. Tends to happen with lifted vehicels with big tires and or with worn front end parts.
Mark