That's remarkable. My Prius V (2013) gets about 49 mpg when I drive 55 MPH on smooth, level roads. A couple of times I've hit 50 mpg. Also, I frequent the Prius Chat forum and I've never heard of anyone getting 60+ mpg. Have you modified your vehicle? Is it a plug-in?
Weird. It's as stock as stock can be. I get 48-50MPG in my normal mix of city/interstate driving. That's on the clock, so de-rate by 5% or so for real MPG as calculated by miles on the odometer divided by gas purchased. Best I saw was 65MPG on the clock over a ~2 hour drive on various country roads coming back to my house, and not flat either (but a pretty minor net elevation change).
