There has been a great deal of conversatioin on the forum about the tranny problems you mentiion. Mine had it too, but I took it in get the update. AS has been mentioned, sometimes the dealership may not know about the update, so you might have to prod them a little. Anyway it worked. No more slamming into gear off idle and more positive shifting. My dealership also gives me a car when service is overnight, or like yesterday when my wife's Envoy was in for running boards, we got a car for the day.
2001 GMC Extended Cab, Pewter (what else), SLT 3500 4X4 Duramax/Allison Line-X, Billet Grille, J&J stainless running boards, Snugtop Tonneau Cover, Striping by Bridge, Jordan 2020 brake controller, Ultra forged alum wheels, 30-gallon cross bed fuel-and-tool box.