Can some of the discrepencies be due to how you fill your tank? Do you top off? I filled up this morning and the pump auto-stopped at 10.59 gallons. I usually don't top off but decided to do it this time and I was able to get a total of 11.89 gallons in. That is a difference of 5.35 MPG on the 518.3 miles I drove on that tank. Depending on the pump, it may auto-stop at different times and that may result in 2-3 MPG difference. My hand calculated MPG (when not topping off) is usually about 1 mpg lower than what my display shows. With the top-off this time, the hand calculated MPG would be 43.59 MPG and my display showed 49.5 MPG.