[spaldam]

The thing I would wonder about is that you only filled it to a half tank, or so you think. I find that fuel gages aren't very accurate when you first start the vehicle. To truly gage you're gas mileage you have to fill the tank all the way and pay attention to how much fuel when it, and how many miles you want from the last complete fill up. Keeping a running total also helps average out the discrepancies