New record again!
 

Just got back from a Thanksgiving trip to Mississippi, 729,2 miles total. On a pure freeway stretch from Vicksburg, MS to Shreveport, LA, maintaining 60mph, with 38psi in the tyres, Trailer Queen returned 20,9mpg! That bests my previous PB of 20,82 despite temps nearly 40* cooler and having more weight in the car.

That is great 20.9mpg, this is the proof that i needed. I had a bet some time ago that mustang can go over 20mpg. Great keep up the good work, post any other new records.

Thanks for the kind words. Some of the lighter (read: non-convertible) bodystyles can be as much as 500lb lighter, especially the smaller '65-'66 models. The '65-'66's also came stock with 2,79:1 gearing as opposed to my 3,00:1 setup. With some carb leaning, I'd expect 22-23 on a light-bodied V8. A six-banger could probably touch 30mpg. And then you can always add some overdrive into the mix...

Congratulations! That's quite impressive for (mostly) 40-year-old technology. ;) I bet you'll break 21 MPG before long. :)

A while back, a friend said, "You bought a Mustang for fuel economy? Yeah, right!"
She was shocked when I told her what I'd managed to squeeze out of it. (And I'd only gotten into the high 29's at the time.)
My current goal is 32 commuting. Probably won't happen 'til next Spring, though...

Yeah, I think next spring would be the best time to hit 21. Cool enough to keep the top up for aero, but warm enough to keep things hot under the hood. If I go on a roadtrip, that'll be what I aim for :)