I'm not sure if I can help you out or not. My '13 has about 3700 miles on it. I reset the mpg reading after I fill up and also calculate by hand. I make a relatively flat 150 mile run on a regular basis. My mpg reading in the car seems to stay accurate, and will only inflate if I start out going down a hill. I have a non PP car, and with my ACC set at 75, I get a computer reading usually of 25.9-26 mpg. My hand calculations usually are about .2 higher, so my computer reading is fairly accurate.
I'm very pleased with that gas mileage and can hope the mileage may get even better as time goes on. I haven't put any mods on my motor yet and am running 92 octane, the highest I can get here.
