First off don't believe the computer, I have hand calculated and compared it to the display and have found major inconsistency between them.
My coach gets between 6.5 and 8.5mpg (hand calculated) depending on travel speed, terrain (hills vs flat), wind, cruise control use, generator on or off (affects fuel mileage as it uses fuel from the main tanks), towing car trailer or not, how much stop and go driving. Tire pressures and even trad design can also contribute.
I find speed to be the single biggest controllable factor that affects mileage. I can get better fuel mileage running 60mph pulling the trailer with my Dodge 1ton diesel 4x4 on it than I do running 75mph with just the coach.
2007 Haulmark 3329DS, Freightliner Coronado Chassis, 515hp Detroit, Meritor Freedomline 12speed Autoshift, 10kw Generator, In-motion Satellite.