I towed a 26' box (30' total length) TT that was around 6,000 pounds with a 2005 1/2 ton chevy 5.3. It did OK locally, but on a 5,000 mile trip through the Rockies, Yellowstone, and glacier it sure felt like the truck was working. Some of the worst was the grind through Kansas with a headwind and slight uphill, where the truck would want to drop into second gear at 60 mph.
I have done the same trip with a 2011 duramax and it was a world of difference. That being said, I am positive that a 2017 2500hd with the gas 6.0 and 6 speed would do quite a bit better than that old 5.3. It gives you a frame of reference. What worked ok with a 12 year old 1/2 ton should be good with a new 3/4 ton gasser, and a dream with a diesel.
FWIW, I am looking at the same basic truck (reg cab 2500hd gas) for my kid who wants a long bed truck. The HD series is so much more truck than the 1/2 ton for not much more money, other than at the pump.
