When towing our 2014 31' Classic with our 2012 Ram 2500HD Cummins, I usually see 11.5 mpg overall, but on level stretches of Interstate, I have seen close to 13 mpg with a rig weight of 19,200 pounds.
For our engine, peak torque is at 1,650 rpm which is 65 mph in 6th gear.
Driving the two lane roads in Texas from Paradise to San Antonio with posted speed limits of 80 mph, I was getting over 17.5 mpg keeping up with the slower traffic driving the speed limit.
WBCCI Life Member 5123, AIR 70341, 4CU, WD9EMC
TV - 2012 Dodge 2500 4x4 Cummins HO, automatic, Centramatics, Kelderman level ride airbag suspension, bed shell
2014 31' Classic model 30 twin beds, 50 amp service, 900 watt solar system, Centramatics, Dill TPMS, disc brakes, 16" tires & wheels