[RMcNeal]

By my calculations, I get 12.8 MPG towing our 3791RD with our 2014 F350 in the southeast US. When I get up to the mountains in WV (usually as far north as we care to go), I drop to about 9 MPG with 7-9% grades.
Not towing, I get approximately 18 MPG around town, and approximately 21 on the highway.
I only tow at 65 MPH max.