Drove the monty home to Louisiana this week. First tank landed me a whopping 20.2 mpg (tire size adjusted), quite a lovely fuel economy. Mostly highway with a few stop and go sections do to multiple wrecks on the interstate. I'll be filling up in the morning for the second tank, which was 160 miles of hwy and about 30 miles of city driving. I suspect the mileage is closer to 14mpg judging by the numbers.
However, both tanks I used mid grade fuel. One from a Krogers gas station, the second from a Shell. Tomorrow the gas will come from an increasingly rare "no ethanol" gas station and will continue to use mid grade fuel.
Unfortunately the numbers from that tank will be useless because we will be taking backroads and flooded farm roads.... good possibility that we may get stuck. Should be interesting.