OK, i feel your pain, i drive a 1995 F-150 Eddie Bauer with auto trans and 154k miles and when i first bought it i was getting the same. im now getting 12 to 17. I also found out its cheaper to do this over time, well not really it just dont seem as bad. Ok, start with basic additives, grab a bottle of injecter and fuel system cleaner and a bottle of octane boost, if you have dual fuel tanks then do one in each tank but if not then start with the injecter cleaner. Give it an oil change, i found that Valvoline MaxLife for HighMilage vehicles over 75k miles, dont forget the filter, also, when you change the oil get some seafoam, might wanna talk to your local auto shop like NAPA for that, its an additive to the oil that helps clean the lubricating system, run that for HALF the oil life and do a regular oil change using the same kind of oil and filter, it will clean crap out of your engine like you wouldnt beleve. Check the fuel and air filters. they hit milage hard. And this is the most surprizing, check your exhaust, if your catylitic converter or muffler is plugged its robbing SERIOUS milage, if its the catylitic converter then you need a new one of the same kind but if its the muffler then i recamend a CherryBomb Glasspack or a CherryBomb Turbo, both exhausts are 20 to 30 dollars each depending on the tube size. These gave me all the boosts i needed, you should get better milage than me when all is said and donre because i have a 302 V8 so i need more gas to make the power where you have the power on tap, beware that you will feel more power with these changes so pay attention.