2021 2500 diesel getting low mpg while towing... ???

[McHenry2500]

My personal experience with my 2500 diesel and stock size tires, best I've gotten pulling my 24' gooseneck with jeep/hay/tractor on it was about 12.5-13MPG.

I'd expect an 8000lb bumper pull camper to be a little worse on mileage just based on it being a brick on wheels....

 

[Razzman]

I pull a 7500lb trailer and also have upgraded tires to 285/65R20. I did have to calibrate as it was off by a couple MPH. That said I average just like the rest, 11-13mpg at 65mph depending on terrain.

 

[H3LZSN1P3R]

If your speedometer is off, your odometer is off. Hence the need to know the REAL/ACTUAL miles traveled ...

Yes, but aside from correcting your Speedometer there is no way to have an accurate relation to miles travelled for your miles per gallon