I actually still feel Firestone has stepped up. I have no problem with them. I stopped in to a totally different location for an alignment check. They looked at my history, re-aligned, rotated, indexed and balanced my tires again. No charge. Vibration still present, but not eliminated (again, this is after a substantial improvement from the drive shaft re-balancing/straightening).
I went back to the dealer again. They said I have 3 bad tires.
So...Firestone, who has invested a lot on their dime (3 sets of tires, including a brand change from Destination AT to Revo2s at no charge, plus multiple alignments, balances and indexes) thinks they are dialed in. The dealer says (again) I have bad tires.
It should not be this hard to balance tires on a truck. I've had multiple trucks and SUVs during the past two decades. On most, I've had either Destination ATs or Revo2s. Rarely any issues...(Ford Expedition, Nissan Titan, Toyota 4Runner - previous vehicles).
The dealership blamed the tires and charged me for the vibration investigation last week.
I've decided I will replace the tires. I'm going to buy them from the dealership. And if there is a hint of vibration, They will own the problem. And since I'm under and extended warranty, I'll ask for reimbursement for all of the vibration related work I've had done that they blamed on the tires.
I have a GM case number, and will also copy them on it.