2005 suburban 2500 6.0 3.73 gear? anyone towed with one?

I have the same year Silverado 2500HD 6.0 410.1. My TT was a Jayco 26.5 weighing 6000lb loaded. The TV handled it fine and most of our towing was in the Western Rockies. You will get between 6.0 and 9.0 MPG depending on terrain. It will handle it quite some better than your 5.3. I did that also.