I fuel up the greyhawk with no problem. Any problems with slow filling has to be a manufactures defect and should be looked at by the dealer.
Gas mileage averages between 8.5 and 9 depending on the mountains we have to climb.
I trained myself on getting better milage by installing Scanguage that constantly gives me the mph, that way my lead foot has gotten to be a light foot.
Jim and Sharon
Jayco 2011 Greyhawk SS31