I just returned from my first trip with my 2011 Duromax 2500HD and 11,000 lb. GVWR 5er. We hit Montana, Wyoming, Utah, and Colorado. We did 5100 miles in six weeks. This had lots of mountain driving - Vail pass, Beartooth hwy., Hwy. 14A in the Bighorns.
I was very pleased to be able to go up all the grades without slowing down at all. Only occasionally, did it even shift down to 5th gear. I was also pleased that we averaged just a shade under 13 MPG for the trip.
2011 Silverado 2500HD Duramax, 4x4, crew cab, long bed
Palomino Puma 253-FBS, 27' 5th wheel
1994 19' Class B on Chevy chassis