I drove 500 miles every other weekend for over 2 years dating my woman and I did lots of mileage calculations. 1, granny driving is for a prius. Get your turbo lit, moderate acceleration nets you better mpg. This has been proven, your best mpg is crusing so if all you do is slowly accelerate then you never cruise. 2, Slower is not better, with 3.54 gears and 35's I get better mpg's at 75 then 70, 1800-2100 rpm, 10 psi, 600 egt. These are the magic numbers to stay under, try driving not looking at your speedo but these three. 3, turn it up. With Edge products at least 6x5 or 5x5 you get better mpg. My right foot is my cruise, factory cruise control and a chip wastes fuel.
So yes hand calculated by gps my mpg is 23 driving 75mph with moderate acceleration. No B.S.