gas mileage
 

1990 f150 4x4 xlt short box 302 4spd auto. i'm getting 12 miles per gallon on a good tank of gas, and thats on the highway. its bone stock, any ideas on what the problem is. my father gets 20 mpg on the highway with his longbed 1990 f150 but its 2 wheel drive. the check engine occasionally goes off and on in my truck could it be an o2 sensor or maybe the fuel pressure regulator, or egr. any suggestions appreciated.
jay