Dude. What does going up a hill have to do with engine speed? And, if you're not getting 400 miles on a single tank of gas, you're either driving like a jackass or in need of a serious tune up. Search and read up some threads here about miles on a single tank and you'll see. I mean, shit. I've left the far, far east side of Phoenix on 3/4 tank and done 85+ with the AC going all the way to Irvine without having to stop.

Think you might do better with 87 octane, NGKs and a new O2 sensor up front, man. Even regularly shifting at 4-5000rpm, you should be seeing more than 300 miles on a tank regardless of what fuel grade you use.

@ deej