What's more fuel efficient? Going up a steep (maybe 20-25 degree hill) chugging along at 35-40 (the speed limit) in a higher gear (therefore keeping revs low) or downshifting to a lower gear, mashing the throttle and constantly accelerating until about 60 while upshifting normally, at which point you're halfway up and then holding that speed until 3/4ths of the way up and then coasting over the crest?

 

Most fuel efficient: You're going fast enough from the last hill that you coast up this hill with the engine off.



Next best thing: Maintaining about 1/3rds throttle, putting the engine under a set amount of load (manifold vacuum) but not enough to go into open loop. Your speed will drop off going up the hill, but you will quickly gain that back when you go down the other side.



Next best thing: Maintaining a constant throttle opening and allowing your speed to drop off.



Next best thing: Maintaining your speed in a higher gear



Least fuel efficient: Accelerating at high revs while going up hill