High MPG (gauge) concern

[rrick]

I just got this 02 auto and I know the average economy gauge hasn't been reset in a while because while going through the torture test/test drive it wouldn't budge more than -.2 out of 19mpg. Now I'm owning, reset the meter and did drive some mixed city and finally a 200 mile 60mph drive (under the best MPG conditions) where the meter rose from 16 to 26 MPG. I'm guessing I'll be very dissapointed at fillup, but if not, is there some vacuum valve stuck open or wrong ATF fluid (TC locks and stays locked, but shifts fine and slips like it should in lower gears). Just worried. I'd rather be burning more fuel than a turbo with a stuck wastegate or transmission filled with honey. Or maybe I should be concerned of aftermarket larger injectors confusing the computer (the truck is completely stock as far as I know and doesn't smoke on the throttle mash). Thanks, want to get on the problem right away, a fill up isn't on the books for a while.

[greasyF250]

M y trip computer is off by 3 mpg, when i hand calculate, its consistently reads 3 mpg higher.

[rrick]

3 MPG high seems about right on the overall last two hand calculated fillups from 17mpg. Calculator is a mess on the highway, a reset while cruising will read 26.