coasting down hills? or speeding down them?

[comrade_charlie]

I drive a turbo 87 300zx, nissan

Any way everyday I have to drive up and down 3 or 4 big hills, then going to my friends house I have to do the same. It is really annoying because I dont know how to drive for the best gas mileage out of my bad gas mileage car, and im always on empty

should I coast down the hill then use gas to go up it, if I coast down and use gas to go back up do I have it in 3rd or 4th gear with vacuum around 20, or have it in 5th gear and have the vac closer to zero? higher rpm higher vac vs. lower high lower vac

Or use a little bit of gas to speed up going down the hill in 5th gear with the vac at 20 and then ill have to use less gas to go back up the hill meanwhile slowing down to the speed limit. kind of like using gravity to shoot me up the hill.

These are pretty big hills so I dont see an advantage in coasting down the hill to climb a huge hill.

basicly show I speed down the hill and shoot up it, or coast and drive up the hill in 3rd, 4th, or 5th gear and at what throttle percentage is best?