i drive in the mountains all the time and when you leave it in gear coming down the other side of the hill or down shift the aveo cuts the fuel to the injectors so you are getting free mpg essentially, and yes under certain conditions downshifting to 4th or even third you can get better fuel economy in the hills, as a result i achieve a consistant 31 mpg in the Rockies and i dont drive nice either, im usually doing 125 kmh or more. you reallly lose mpg at those speeds.