Interesting timing for this question. Historically, when my coach was gas powered I got 7-7.5 and would tell those at the gas station something to the effect of "Well, I don't commute with it so it doesn't much matter what it gets, but it gets 7-7.5 mpg".
Since I made the engine conversion to the Duramax, the question has come from my fellow FMC coach owners. The documented cumulative fuel mileage to date, with 14,585 miles on the conversion, is 14.23 mpg. This includes a trip from the west coast to the east coast and back. For the last five tank fulls, which is when I switched the Banks tuner to the "economy" mode, it has averaged 15.03 mpg. Those fillups got me from the east side of Michigan to Brooks, Oregon which is just south of Portland.
While those mileage figures are good, it will take a lot of miles to recover the cost of the conversion. I need more miles on the economy setting to get a solid "average" number.
