So, I took my car on a nice drive last Saturday. Before heading out I went to the gas station a mile from my house and filled the fuel tank. After that, I took my trip, which involved a good mixture of driving, it was mostly country two-lane travel but there was also a fair bit of stop-and-go and some highway motoring.
When I got back to my neighborhood I'd driven 92.2 miles (according to the odometer, which I think is conservative according to GPS). I went back to the gas station and filled the tank again, which required 4.317 gallons of 87 octane. According to my math, which isn't very good, I averaged better than 21 miles per gallon. HOW IS THIS POSSIBLE?

I mean, I'm not complaining, but something doesn't seem right.

It shouldn't be
that high, should it? And I'm not afraid to rev it up or cruise at 65 miles an hour.
My car's engine is basically stock aside from dual exhaust, an 80-thou overbore and 12-volt electrics. It's got a 3.78 rear-end and NO overdrive.