I get on average 290 miles a tank which works out to be between 27 - 29mpg. Mine is a Zetec with 111,000mi - Injen intake with K&N cone filter, Magnaflow exhaust, Mobile 1 full synthetic oil and tranny fluid, Royal Purple power steering fluid.
I do have a lead foot and do mostly city driving, sounds like you do mostly highway driving.
Hatch Nation #8
September 2012 Ride of the Month