It's kinda like the federal government budget...you get numbers, but they are not reliable. I use a credit card for all my fuel and write the mileage on each receipt. Every so often, I collect them and figure my mileage.
The day I got my F-350, I shut the overhead idiot display off and it's been off since. If I had been able to, I would have selected an XLT rather than the Lariat. The overhead display is worth than worthless, IMO.