I'm still getting used to ours in our 2000 Jayco, but so far have been very pleased with it. My only wish is that it sounded a little more "muscular" on takeoff, but that's the only complaint I have. The sound reminds me of my '77 Dodge Tradesman van that had Chrysler's Slant Six.
Between 55 and 60 MPH, I get about 7 to 8 MPG. Running a little faster than that puts us closer to 7 MPG. Still, for something weighing north of 12,000 pounds loaded, I'm not upset by that at all.