Trip Computer
I just built a spreadsheet with my fuel data since I bought my 2005 V6 4x4 in October. I reset the trip computer each time I fill up, and the avg speed has been all over the place (and probably correct). The range has been from 15 (an offroad trip) to 70 MPH (a highway trip).
As for mileage, it's been a bit disappointing. The calculated mileage has averaged 16.8 MPG in mixed driving. My best tank was 19.9 MPG, which was virtually all highway miles, and averaged 70 MPH on the trip computer.
As most people know, the trip computer MPG is always higher than actual. In my case, it's been from 8 to 14% high. What's interesting is, the higher the average MPH, the greater the error in MPG!
Enjoy!
-- Jim