I get a max of 18.2 mpg on the highway. Ive noticed when I move the shifter to Manual shift its always in 6th gear. I try to up shift to 7th or 8th and it wont do it. This is at any highway speed. The manual says you should be able to up shift all the way to 8th. am I missing something here? But it makes sense that my highway mileage sucks if it wont go past 6th gear.