I had an 08 GMC 3/4 ton with the 6.0 Votex, pulled my camper very well but averaged 8mpg, not pulling anything I got around 13mpg. Rode rough when empty.
Traded it in, in 2012 for a new Ford Expedition with their 5.4 V8, now I get 10mpg towing and 19 on the highway, with a much better ride.
The GMC was a good truck, just could not afford to feed it.