James is giving you great advice. In my opinion, you will be happier towing with the Denali. While you may lose 100-150 lbs in payload, from a practical standpoint, the extra horsepower and torque make a big difference in how much time you can stay in a higher gear. A few folks here have said they have towed with both 5.3 and 6.2 trucks and observed that the 6.2 just doesn’t have to work as hard.
I prefer the AWD for towing as well because it’s full time and splits the torque load that each drive axle has to take, which for me has resulted in longer rear axle life. One member here reported having to replace his rear drive axle 4 times when towing heavy with a part time 4wd system. The AWD is an extremely reliable and durable system as well.
Also, it’s a simple matter to add a trailer brake controller to one of these trucks because the wiring is already there. But as I mentioned before, you would lose the benefit of automatic sway control that the factory controller offers, which could help you avoid a disaster in emergency maneuvering.