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I run 87 in my 3.5, just returned from Florida and I had 18mpg highway. This was 70mph w/aircon on 32's. During my 1hr mixed commute I get 16mpg.

My high mpg was around 21mpg with the factory 265/70-15's


this is the exact mileage I get on 87 also. I know everywhere in the manual and the gas lid it says to run high octane. i have run 87 for the past 4 years with no knocking unless I get cheap gas. Will it get better with high octane? I don't know cant afford it.