I'm in the don't worry about mileage camp. RV'ing is not an MPG efficient past time. The best way to improve MPG's is to slow down.
There are many factors that effect MPG's, many I can't control. Wind,terrain traffic,weather,altitude are all factors.
The $$ difference between a couple of mpg's is negligible as mentioned above for this reason I find mpg discussions amusing.
In the end my advice is don't worry about it, push the tow haul button to allow your transmission to shift more efficiently while towing. Sit back,relax and enjoy the ride.
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