Originally Posted by Fredog (Post 418716)

well, my truck seems to have settled on about 5.3 miles to a gallon, it doesnt matter if I go 55 or 65 or 75, it gets about the same. Any suggestons on what I might do? I know I need to get it put on a computer but other than that, what should I do?
it's a C-15 cat says 435 on the tag, but I dont know if it's been turned up. has 13 speed and 3.55 rears.

Originally Posted by GMAN (Post 418849)

I just thought of something, Fredog. When you check your fuel mileage to you rely on the computer or odometer?

Originally Posted by Heavy Duty (Post 418873)

Check the charge air cooler, if mileage doesn't improve at slower speeds it is probably leaking. Higher RPM's help it overcome the leakage. Cheap to check, I would do it first.

Originally Posted by Heavy Duty (Post 418873)

Check the charge air cooler

Originally Posted by Kranky (Post 418889)

I'll second that.