Truck is an 80k mile original F150 4x4 w/5.0 auto. It never seemed to get the best mileage but I've checked it (3 tanks full, by odometer) and I'm getting anywhere between 8-10 mpg which seems pretty low for a truck this size. Hell, I used to get a steady 14mpg from my '96 250 w/5.8. What gives? Truck is never loaded and well maintained. No Check Engine lights and giving no codes. Maybe it's the gearing?? I'll post a pic of the tag-I'm not sure what "19" is for an axle code.

 

peg leg 3.55, stock tires? last O2 sensor installed, and tune up

 

Larger tires, and I'm *pretty* certain that the 02 is original...think that should be changed even though no codes are being thrown?

 

check fuel pressure, just to see where its at, and you could watch gauge and see if it goes down fast, or slow, could have leaky injector/s. I had 3, and I still got 11mpg, with 31's and before leaks, got 12-13mpg