The best way t get good mpg is to simply use the technique a driver's ed instructor told me many decades ago -- just drive as if there was an egg between your foot and the throttle.

Now, I am not advocating this method, as it takes away all the fun of driving... but if you want the absolute best mpg, that's how you do it.

Cruise control does not work the best in non-level situations, as a constant speed is not the way to get the best mpg in hilly country. Cruise applies too much throttle on the upwards part of hills or rises to maintain a constant speed "no matter what," even downshifting to keep the speed up. The best mpg in hilly country is to slight let off the throttle on the upwards bit (avoiding downshifts to the extent possible), slowing 10-15 mph by the time you reach the top, and gently picking-up extra speed with a little extra throttle on the downwards slopes to "get a run" on the next hill.

Again, I am not proposing this, as (a) it's not much fun (b) the changes in speed irritate other drivers, and (c) police like to nail people on the bottom of hills where you'd have the extra speed... but that is the method which provides maximum mpg.