Quote Originally Posted by Raque Thomas
10mph make THAT much difference in mpg?
Drag is a funny thing and actually increases exponentially after it hits its design limit. Plus with all our ground clearance we've got quite a bit of undercarriage drag as well to add.

I've found 70MPH seems to be the "economy" ceiling for highway cruising. Above that you may get there quicker but at the expense of extra fuel.