We have the 5.9 in a 40' coach, always drive with full water of 80 gallons and always do the 70 mph speed limit on the interstate. Even with a good head wind the lowest we have ever gotten is 7.9 the most 8.9.
We had a 32' V10 we drove the same and mileage was between 5.5 to 7.5, it was all over the road, a rough ride and a screaming engine that put out so much heat we often had to drive with the genny and the roof A/C on. Once stopped the heat from the drive shaft would heat the floor from engine to the rear wheels, even with both A/C's on it was hard to cool the interior down.
Happiest day was trading in the 2014 and buying the 2007 diesel. Granted with an older coach there are things to update. However its a joy to drive, we talk now no more shouting, no more jarring bumps.
Just my 2 cents.
