I have a 1986 ford F-150 4x4 with the 5.8 H.O. engine in it. As far as i can see it is completly stock right now. The thing is is it only gets 13 miles per gallon. I thought there must be something wrong with the truck but when i went to fueleconomy.gov and looked it up it said right there in black and white that the fuel economy was only 13-15 mpg. My question is why such crappy gas mileage?? Does anybody know of any way of getting it to perform at a decent mpg. Would better breathing make any difference at all. Better KN air filters? Headers? Would they make much difference. And what is the thing with the 5.8 liter H.O.?? Why is it HO? And is it worth keeping? Thanks in advance guys