Cold weather, cross winds equals 8.5 mph.

After stressing out about gas mileage when we first started RV'in in the '80's I've since figured out that if I'm going to enjoy the travel, I have to forget about it. except for once in a while to get a read on how the engine is performing, I just stick the nozzle in set the automatic fill thingy, and go wash the windshield or go buy something or head for the head. Once its full and kicked off, put the hose back and go on our way. The DW pays the bills, so since we use a gas credit card, I never know how much we've spent on gas and she doesn't care either, as long as we have enuff to get there, and back. I think the last time I checked it was about 9.5.

I have time to do all three things while its filling cause the Suburban has a 42 gallon tank.