Bought my truck in January, been putting all the gas receipts in the center console, just got around to typing them all in and figuring a gas mileage. Lie-o-Meter routinely says 10.5. I also didn't write down the mileage on all the receipts, so these are 7 and 3 month averages. Checked the receipts vs the bank statements and I lost one receipt in June for 97.08, so I put it in as $3.65 a gal for 26.597 gallons.
Overall if the 10.39 mpg is accurate I am really happy since it's a stock 2000 truck with leaking exhaust headers, and I drove it 2000 miles with 2 faulty COPs. (Although it shuts off the fuel to those cylinders...when they are failed.) Most of the failed COP driving was in the past few months which showed a reduced MPG of 9.79, but could be because I was using the AC more.
Someone else who keeps records as detailed as me. I was taught by my dad, who's a mechanic, when I bought my first car to try to keep track of your gas mileage as it may be your first clue that something is wrong with your vehicle.