Hi Tar----In 2013, we went from a Chevy 2500 8.1 liter gas/Allison Tranny combo to a 2013 Duramax SRW 2500 HD 2x4. Per the DIC, I have seen 11.5-14 mpg. towing. 19 to 22 mpg no/load on the freeway. I tow a 33ft. 11k fifth wheel. The torque and power of the diesel plus the ability to manual shift while using the exhaust brake in hilly/mountain conditions, make for a greater towing experience. Took a 10k mile trip last year and with pre-planning, RV parks and fuel stops were not a problem. A good day to you--happy travels. Ken