Gas Mileage with new exhaust??

[marnepup]

I got 21.5 on the highway on 93 octane (now I live in 91-land) at sea level, with the cruise set at 80...24 seems a bit high. Interestingly, My miles per tank dropped from 340 to 280 when I gained 5000 feet of altitude and swiched to 91 octane. The price of gas is below average out west (states like CA and CO excepted, of course!), but consumption is higher due to the altitude (and, for premium, the lower octane), so you probably pay more per mile, not less.