'97 C5 Corvette. Bone stock. 278 miles from Brucken Germany (elevation ~350m) to Grafenwoehr, Germany(elevation: ~412m). I have not verified at the gas pump, yet. The spedometer is accurate to within 1kph using a GPS as a reference.
I generally kept the speed around 50 mph (80 kph), but it varied depending on traffic, hills, construction etc. Stayed between 40mph and 65mph and stopped 3 times during the trip. No drafting. Used the cruise control early on in the trip, but maybe 80 miles into it, I decided to go for fuel mileage and wanted to modulate throttle myself.
Previous best was 38.8 mpg as measured at the pump vs. the odometer. The driver's information center read something like 37mpg. That was on a 600mile trip from FL to OH.