9700 miles on the odometer. 2LT package with 6AT. 200 mile round trip on interstate. Had 1/4 tank 87 octane top tier fuel when I left. As soon as I got on the interstate and tranny shifted into 6th gear, I reset the mpg calculator. 70mph, no stops, hilly terrain. No a/c, 31.9 mpg. Quit calculating when I exited the interstate. Filled up with 93 octane Top Tier fuel. Same reset on mpg calculator, same cruise speed, ect. Got back home 37.6 mpg. Had tried experiment before with 89 octane. Could see no verifiable difference. Just an fyi.