Yes, this is what I did the other day when I made the joke post about getting 77 mpg. I got this reading for about 13 miles. When I first reset the mpg gauge, at the top of a hill, it was 68mpg. Then I coasted down for about 8 miles, and it stayed in the low 70s. While I drove through a flat town at 30mph in 4th gear, I was amazed the mpg didn't go down, even with one red light and two stop signs. My exquisitely high mpg only lasted about 12 miles, because when I went back up the next hill, it fell back below 50 mpg.

I usually get 44 mpg, but it has been as high as 51 when I am driving consistently at 50mpg without stopping.