Congrats, I would think you should find the Denali as a good replacement for what you are towing. I too really liked the GMT800 SUV's, but you can't beat the improvements and additional safety features with the newer trucks.
As mentioned, that 6.2L has 60+ HP and two extra gears while only being down 33 #-ft of torque. I am thinking the extra gears and HP will offset the slight decrease in torque. The 6.0L in my Express was happy towing in 5th gear all day long towing a 7200# TT.
I am guessing you will also appreciate the increased fuel economy too. When we got our XL this past November I would have liked to have gotten a Denali, but I decided I really wanted the selectible transfer case more than the 6.2L.