2011 Lancer GTS fuel economy
 

I have a few quick questions. Just got the '11 GTS and found it gets very good gas mileage for the first quarter tank (up to 36 mph highway), but then it dips down to around 29 mph by mid-tank, and then settles a tad lower by the bottom of the tank of gas.

Is this to be expected? If yes, does this mean my best fuel economy would be while I maintained the fuel level over half a tank?

Also, which grade should I use? The book says 87, but I've heard mid-grade 91 is the better way to go. Confirm or deny?

- East Blue