On one leg of a return trip
> several years ago from the Northeastern US (back to Dallas), with four
> passengers and quite a bit of luggage and camping cargo in the back, I
> somehow managed to get 28 mpg.
>
> This with the 3.5 liter V6 Acura engine, A/C going full bore, and driving
> mostly around 80 mph.


A small tailwind can make a big improvement in mpg. A small headwind
can take a pretty good toll as well.