Ive got a 2001 F-250 with the 7.3l Powerstroke, 3.73 rear end, 4" lift with 35" tires. I bought the truck with the lift and tires.

If you drive 55mph with the cruise on on flat highway, it will get 15.

If you drive 65mph on flat, it will get 12

When pulling my 27' baja (6k?) it gets 8

Is this normal. Is it the bigger tires bogging it down? Or is there something wrong I might need to check for. Pulls it great, runs great.

Big tires, small rear-end ratio certainly doesn't help.
It does seem excessively low even for that combo.

Remove the muffler and straight pipe it or if you don't like the sound then I reccomend installing a Magnaflow muffler. If you do this and install a K&N air filter you would gain almost 2 mpg. I have done dozens of these and all got 2mpg better and one 03 Dodge that got 3mpg better.

Could be the tires. I did 600 miles in the last three days , mostly flat and not towing , but at least 100 miles at 75/80 mph the rest 65/70mph and still averaged 19.9 overall. Does your truck also have a different chip. Mines an F350 x cab srw 4x4.

No chip, and its a srw f-250. I have not seen the day it gets over 16

BR.............Do you have any idea what size tires came on the truck as "stock". My guess is the new final ratio could be down to 3.2someting with the 35's on it. (assuming the stocks were much smaller).

But yes, going to a larger tire diameter does decrease the final drive ratio.



Bob

Has the speedometer been recalibrated? On my diesels, if I don't keep the fuel filter changed and injectors clean, the mileage goes down.

Has the speedometer been recalibrated? On my diesels, if I don't keep the fuel filter changed and injectors clean, the mileage goes down.

Ive never changed the fuel filter. How do you clean the injectors? (ive only had it 10,000 miles and im sure it needs one)

Ive never changed the fuel filter. How do you clean the injectors? (ive only had it 10,000 miles and im sure it needs one)