I have a 1500 Megacab Hemi. I love the heck out of it, but gas mileage does suffer. I average around 16.5 combined mileage, but when I towed a buddies Honda Civic race car (completely stripped, race trim) in an enclosed trailer, mileage dropped to around 7 on the freeway.
(And yes I know, "A HONDA!" Naturally aspirated, 13.10's in the quarter. Fun little car, and still gets better mileage than my truck )

 

Must have been a good sized enclosed trailer. I tow a light 18ft. Dual axle enclosed car trailer and get about 12mpg on the freeway at 60mph.

 

seriously? i had a 2007 megacab 1500 hemi before i got my 2007 megacab cummins and i got 12 mpg on the freeway at 70 mph not towing nothing maybe i could get 14 at 60 mph.

 

Well I have a 1500 Quad Cab, so the difference in weight with the same power plant is substantial. I can get about 18-20 mpg on ling road trips @ 70mph hand calculated.