I use the Range AFM delete on Interstate trips....................I'm leary of AFM to function much more than 100,000 miles effectively. And I don't like the idea of cylinders not firing/coasting along................as I believe the engine will wear in/out unevenly over time.
That said; if I keep my speeds under 70mph on the Interstates, I can still pull 21-22+mpg (HAND CALCULATED FOR THE WHOLE TANK) in 100% V-8 mode.
One trip running North on I-95 from FL thru GA thru SC; I pulled 22+mpg running 80+mph with a 10-15mph wind at my back............it's a rare occurrence that I have the wind at my back when traveling.............took advantage of it there!!!