Right after purchase, the truck began to perform as if pads/rotors were metal-on-metal. At moderate braking they would shudder and give growling noises. Dealer "burnished" brakes. (Meaning drove it around a lot holding brakes!) When I picked it up, the problem was gone. Next drive, and all subsequent drives, scrubbing returns unless I apply harsh braking repeatedly on that drive, noise then stops, only to return next drive.

Went with the tech and dealer president - they asked me to "Give it 1200 miles". I say: "Then what?" Their answer: "These are new designs - totally electric brakes with new pad compound, GM is working on a second pad compound." I have no assurance they'll solve this, but reading now of many total brake failures , some resulting in collisions.

I despair of a remedy . Truck just rolled 600 miles, I have no faith they'll get this any time soon.

Not a good way to spend soooo much money!

Update from Oct 28, 2021: Next attempt to remedy was a four-hour wait at service while pads were removed and "treated with some after- market "potion". This cured the problem for as long as the potion lasted, but heat and wear had the brakes behaving the same way. Even though the potion didn't cure the problem, it proved (to me, at least) that the problem WAS the pads. So the dealer wrote some unclear phraseology on the diagnosis to get GMC on board, the pads were replaced at about 600 miles and the problem disappeared. Truck now 18 months old, 6,500 total miles--brakes have been fine ever since.