Help with my truck..Please

That is a big drop in mpg's. I have not seen that much difference in my own driving, but speed can make a difference. I may be that you have low gears in your truck. You should be getting higher mpg's at 65 than 5.2. Of course, terrain, type of trailer you pull and weight also play a factor in mpg. You might also notice your driving habits. If you are inconsistent in your acceleration and braking your mpg will suffer. I think there is a website which discusses mpg and rpm and gearing for optimal fuel economy. I don't remember the web address. If you can't find what you need on the International website, you might try your local dealer and ask them about your gearing and what you might be able to change in order to improve mileage.

 

Going off your numbers and assuming that you have lopro 22.5 tires, you have 3.70/3.73 gears now.

 

He didn't say what trans he has, considering 435 hp Cummins I'm guessing it's fleet spec with 22.5 lp and maybe even a 10 direct which may already have a fast rear end if its a direct drive ... Need more info ...

 

If your tires don't have 11R in front of 22.5 then they are lopro.

 

If you were to put 11R 22.5's on it would drop your engine RPM at the same speed compared to a lo 22.5.