I realize this thread is several months old, but we didn't have our Greyhawk when it was active. Just returned from our second trip from Raleigh to Atlantic Beach, NC and back. Our 2014 Greyhawk 31FK averaged 8.3 mpg, we were not pulling anything, it was very flat terrain, and I never exceeded 60 mph. Hopefully this will improve slightly when the Ford V10 breaks in. It has only 1300 miles on it now.
Just adding this note in case a future searcher encounters this thread.
I have a 1999 283G Eagle. Just got home from a 2000 mile round trip from south Louisiana to Kansas City and back. Drove all types of terrain. Somewhat loaded heavier than normal and not towing a vehicle. I averaged 7.5 mpg. Drove at an average speed of 63 mph and still had two rear tires with tread failure...oh well!
Jeff and Deidra
1999 Jayco Eagle 283G Motorhome
2015 Ford F350 Lariat Ultimate
2014 Heartland Cyclone 3110 Toyhauler
Baton Rouge, Louisiana