Ok, so picked up the Denali this afternoon, and went for a drive. I took the exact route that used to highlight the transmission issues, and prompted my trip to the dealership.
The service invoice says the following, "Roadtest to verify concern, check ECM/TCM with latest software, warranty claim code #---------, roadtest vehicle to specified temperature, perform fastlearn, roadtest vehicle and set transmission clutch volumes for individual clutches, learn clutch return spring values, verify repair."
There is a noticeable improvement in drivability. The shifts are much smoother, the rattle from the AFM (during the V8 to V4 switch) is now absent, and the overall vehicle, believe it or not, is much quieter. There isn't that "bogging" feeling that I got (no other way to describe it, it felt like the transmission was in too high a gear at low throttle on an uphill grade).
I'm quite surprised that a software refresh could make such a change.
It feels overall much better. Pretty happy right now!