My "other" car is an '86 Ford LTD mid-size w/3.8 liter V6 (around 120 hp) & 3-speed atx w/ torque converter lockup. Gets as high as 22 mpg for straight freeway down to 16 for city.
Sounds like you're doin' better than that!
Just for comparison, my '99 SE 4 cyl atx has reached as high as 35 mpg highway (that's w/ 4 on board & a trunk full of luggage). I've driven from Columbus OH to St. Louis MO (approx 400+ mi) on one tank of gas (two on board this trip).
