Best magnum MPG?
Just for giggles, I'll throw in my mom's 2002 QC (quad cab) Dakota with a 3.9.
Not sure on the rear gear for that truck, but on the same "test loop" drive routine it got 18.25 MPG. Again, not a crazy difference for such a drastic decrease on engine size and power. Of course, I'm sure that truck is a bit heavier.