I will average 9.5-11 mpg when towing with my Duramax, 18.5-19 mpg when empty. I bought it to pull, not as an economy vehicle, and it darn well pulls. I don't care about the mileage. When it gets low, I fill it up and drive some more. If great mileage was a concern, I would sell the truck and rv and throw a tent in my Malibu. Not gonna happen...
Becky, Bob and Taylie & Bode
2009 Silverado 2500HD Duramax/Allison
2014 Heartland Sundance XLT 245RL