RPM and mileage
I think I read somewhere the official speed at 3000 RPM is 72. My speedometer and tach show 75 MPH at 3,000 RPM. Each 1,000 RPM seems to be about 25 MPH by my tach and speedometer. At least at 50 MPH and 75 MPH.
On the highway long hauls running 70 and 75 MPH my low fuel light comes on around 150 miles maybe just a little more. On roads around 55 or so MPH The light may go as far as 170 miles before the light comes on. Of course the obvious is that varies a lot with traffic, hills, and you right hand.