I got over 70 mpg on the parkway this summer too. It was twisty and steep. I guess it is just because the RPMs were lower, because it certainly seemed like it was working the engine harder going up those mountains but on the way down it coasts mostly so I guess it makes up for it.(and then some evidently) I do mostly highway driving at higher RPMs and I just hate that I only get around 49mpg on a relatively flat highway. I wish I worked up in the mountains. If I change the gearing will it get better gas mileage on the highway since it is at a lower RPM like it was in the mountains?
Seriously, I shouldn't complain. I would not get 49MPGs in my car. I get about 35MPGs on the highway.