Resetting the timing and synchronization of the motor did the trick.
Thanks to HUMTECH and my local ex-Hummer dealer (Criswell Performance) I was able to get the official GM instructions on the process. At first it seemed a little daunting, but literally took 30 minutes and involved 8 bolts/screws (4 of which I think I could have left in.) My biggest concern was that it would be difficult to get to the motor, but it's completely visible and accessible once you remove the ceiling console (see image).
I'm including the documentation below...I honestly believe you can skip step 1 (saving you those 4 bolts I just mentioned). I saw no reason or need to remove the glass to re-sync the motor.
Before starting, make sure you adjust your sunroof to a position where the glass is firmly seated and you get no (or the smallest amount of) give when you try to move the glass up and down. Mine was seating a little high when it thought it was closed, like it was starting into the Vent position, so I kept tapping the Open position on the switch until the rear of the glass hunkered down a bit more. At this point the glass became much firmer, then I started in with the process below.
Once complete I made some adjustments to the height of the glass using the four torx where it connects to the track, opened and closed the sunroof a few times, and took it for a test drive. At 75mph...no bouncing, vibration, movement, or noise.
FIXED.
