Last December we bought a 2014 GMC 2500 HD 6.0, 6 speed, 4:10 rear ends, 4X4 gasser the work truck model because it suited our needs. Only have about 1500 miles on the truck and have been babying it a bit so far. Averaging 12-13 running empty and have only made one RV trip just last week. Three hundred mile round trip over 4 mountain passes averaging 4K high with 7000K trailer. Towing speed limit here with trailer is 55. we took the trip pretty slow because of icy roads and probably averaged 45-50 mph. Going over we got 9.8 mpg and coming back we averaged 10.3.
We love the truck and are happy because the towing mpg is just about the same as the 2006 GMC 1500 we traded in.