my 1988 GT 5spd CONVERTIBLE w/ 3.55 gear and 200,000+ miles with stock unrebuilt everything got 27mpg REGULARLY on the highway at 65mph and 20-21 in town. I changed the speedo gear and verified it to read correct mph too. I used sythetic oil 10w30, 1/2qt duralube every oil change, 6k oil change intervals, synthetic gear lube and trans fluid, in fender cold air, stock fuel pressure regulator etc... The one thing I did notice that helped was MAC underdrive pulleys - I was expecting more power but I did not notice any power difference but I did notice a big change (23 changed to 27mpg) in gas mileage. I could attribute this to the fact that I also replaced the radiator with a three core unit, new fan clutch, new aluminum water pump, new stock setting thermostat, new clutch, timing bumped to 14 degrees advance, 16 inch pony wheels (feel so much better driving than 15's) 35 psi tire pressure, repacked bearings, new plugs, new wires, new cap, new distributor, new motorcraft ignition module, etc.... to get it in top running condition. --- I have no idea how this got posted to this thread - I was responding to a thread that was saying if you could get 30mpg in a 5.0 -- sorry.....