Skepticism of exceptionally high Scanguage numbers?

[Sludgy]

While the Scangage is incredibly useful as a monitoring and feedback device, it overstates my F350's mileage by about 25%. I get 19-20 highway mpg in my diesel at fill up, but the Scangage trip meter says 25 mpg or so.

BTW, I spoke with a servive rep at Granatelli motorports, and they are going to send me a replacement module to see if my the truck stops misfiring and gets the promised mileage.