Hi guys, I always wonder how come my present car and my former car always get better mpg during 80mph compared to 65mph. Present car: Cadillac CTS 2005, 3.6l vvt 65mph/2100-2150rpm=28-30mpg 70-75mph/2300-2500rpm=24-26mpg 80mph/2600-2700rpm=29-34mpg I did some test on the same road, same day, same weather, cruise control was set, same outside temp and humidity(or almost). Former car: Buick Regal 2002, 3.8l 65mph/1750rpm=25mpg 70-75mph/2000rpm=28mpg 80mph/2100-2150rpm=32mpg BTW, the data I give you is from the DIC for the CTS. As for the Buick, it was the calculation from gas bills compared to miles I did. I am always curious why do I have to go faster to save fuel. Kinda weird to me and thats why I'm asking here!