last couple 5th wheels were 15k lb or above, pulled them with a pile of different tow vehicles
- ram 2500 with the 6.7 diesel
- gmc 2500 with 6.0 gaser
- volvo 610 with cummins ISM
The 6.0 gaser was under powered and really didn't like wind or hills. Mileage in the 4-6mpg range, it wasn't enjoyable at 15k lbs.
The 6.7 diesel had plenty of power and pretty decent engine braking. When the load cleared 20k lbs more truck would be better, but it wasn't a power issue. More so braking and engine braking. 15k lbs it would get 7-9mpg.
The ISM was great for eating miles on the interstate. 9-11mpg with the 24k lb trailer, insane engine braking and very stable.