I am guessing this is a miscalculation.
It seems the highway estimate is 22 mpg highway, the best was a 25, according to FE.gov
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Fuelly says the best ever was 33 mpg, but it seems like a miscalculation, too, as all their pattern of fill up (time wise) didn't change, their miles were completely in line, but a 2 was replaced with a 5- the rest were around 15 mpg. Of 62 tanks, it was the only higher than 19.2, so it doesn't seem like steady improvements in aero/driving.
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It seems very unlikely the vehicle is performing that way, from my personal experience and research on the net (not that you couldn't get it there!).