MPG to good to be true??

[MuddenJeff]

Recently recived the CTS for my 2004 F150 FX4 5.4L CAI and cat-back, with 3.73 gears and tires that close to being stock. I didnt update using fusion yet becouse of all the recent issues but I did flash my truck with lvl 2 87 oct, and the current tire size. At the time I didnt know about the squish factor but I will be messing with that shortly (multiplying value by .97). Before the programer I would resent my trip meter to zero on each fill up and calculate my MPG, I was getting anywhere from 15-17 tops. Now with the programmer, the programmer is telling me I am in the 24-26mpg range which sounds to good to be true. I have noticed the dash spedometer reads a few mph off from the programers speedometer (ruffly dash @ 63 when programer at 60 and it gets futher off the faster you go).

I know I havent yet adjusted for squish yet but am I missing somthing bigger? I never could figure out if the programer is set with the correct gearin setting (3.73). I am almost ready for the next fillup and I will beable to compare the manual calc to the programmer and see if it is tracking the same.

Will your programer re-programmer you dash instruments? i.e. your dash speedometer and odometer? or is that a something else? I noticed the trucks odometer doesnt track perfectly with the interstate mile markers- but if I can get a hold of a GPS unit I might beable to figure that out better.

Any feed back would be helpful, Thanks