I made a 375 mi. round-trip last weekend, on the way up, set the cruise to around 80, got 30.xxx MPG on the way there. Interestingly, I set the cruise to 73 on the way back, only got 27 MPG... might not be related, but I seem to get better mileage at speeds closer to 80. With some city and a lot of highway, I usually average about 24-26 MPG.
1994 Super Coupe ('93 5.0L swap), 1990 Tbird 3.8L, 1982 Honda CB900F, 1972 F-100 SportCustom 4x4, 1970 Chevy Custom Camper / 20