I have a '00 XJ with 57k, 6.5" long arm, 33" MTR's, 4:10's w/lockers. Corrected speedo/odo. I do a lot of around town driving (moderate traffic lights, averaging 45mph in between lights....12 miles on way to work) and I filled up and calculated my mileage this morning. I averaged 17mpg. I'm...