All of these numbers are exactly the reason I bought a '07 (on and '06 chassis) WBO View (a Dodge/Mercedes Sprinter 3500 cab/chassis) I have early on decided I would not accept single digit fuel mileage. I haven't used the View yet, bought last fall and been slowly fixing and cleaning on it, and about ready to take the first trip, but on the trip up from JAX I got over 14 mpg on the first tank full and the first hour of it was done at about 70 mph before I slowed down. Third tankful I have been burning out of it driving locally as I need to drop the tank to repair a leak at the pump mounting seal, but staying at 55 and below, the mileage on this third tank full is clearly better than the second tank full, which was 17.2 (I went 248 miles to exactly 1/2 full mark) on this tank full, I went 300 even to the 1/2 tank mark, so I could be close to 20 mpg.
Charles