you would use the least fuel if you popped to neutral at the top of the hill and shut off your engine, coasted until you needed to accelerate again, restart engine and pop into gear... now would you run the risk of a speeding ticket or an unsafe speed for a turn... I don't know... but you would use less fuel for that trip than the other method. I've done a great deal of fuel economy study, i did some work for aptera before they closed their doors, and their car was getting 200mpg equivalent. I wish i could get my grubby mitts on one of their mules... they had about 12 iterations at their plant in carlsbad, super aerodynamic and super lightweight, had a drag coefficient lower than lance armstrong at full tuck.