Just finished a 1700-mile trip to Illinois. Including the crosswinds, 10% ethanol fuel in Illinois, hills on I-55 on the way to St. Louis, lots of construction, a couple of 30-minute backups, and a few days of city driving only. I still got around 20 mpg overall. Not bad on a set of Revos.
Because the state police tend to be very efficient along the route, I kept to the posted speed limits using the cruise control.