well i just got back, and double checked this time with my GPS. filled up at a station on 21 west. from there went 78.9 miles to the station right by my house where it took 3.089 gallons to fill my tank back up. that comes out to 25.54224668 miles/gallon. and on the way back i had cruise at 70 the whole time, exactly 2k rpms. not sure exactly what's going on but the drive is mostly flat the entire way, wind could be a factor but i don't know. all i know is i did the math and this is what came out
