My gas mileage is improving

[jdlmodelt]

I live in Colorado. My commute is 27 miles one way. I'm at about 6200 feet. My commute is all highway miles. I get between 28-31 depending if I have to puts around town before heading home. I have a 99 with the 2.5l and a 5 speed manual. The highest octane fuel I can get is 91 and it has up to 10% ethanol in it. I accidentally put 87 octane in once and it felt like I was driving a Honda Civic. The power drop was frightening. I added octane booster and kept adding 91 as frequently as I could to get that low grade stuff out of there.