With my Contour V-6 ATX I got 32mpg on the way back from picking up the car in Georgia. My first trip to the Dragon I averaged 28mpg under very aggressive driving conditions in the Smokey Mountains. The return home first tank I got 33 mpg, the next tank, 31 mpg IIRC. My car was stock except for a SuperChip & modded Y pipe. If you've got headers, a free flowing exhaust, & a good intake, I can see getting a few extra mpg on a tank or two - especially with the cruise control on.
I don't know what combination of conditions makes it happen, but I suspect the mix design of the fuel I was getting had a lot to do with it. I get CRAP mileage here in Florida, typically about 22mpg mixed driving.