I have an 89 F-150 4.9 with a c-6 auto. On a good day i'll see 13MPG, so i'd say you aren't doing too bad. I used to have a 86' F-150 with the 4.9 and a 3-speed overdrive. That truck would get much better mileage, more in the range of 16 in town or 20 on the highway. Overdrive really helps!