I try to keep the highest vacuum possible at speed. This becomes difficult with hills/mountains, sharp corners, ect.
Going up hills... define hills, here we have 8-10% grades... keep your speed constant. I find dropping a gear to hold your speed nets the same results as bogging down in a higher gear with your foot to the floor and slowing down necessitating a downshift anyways and using more throttle to regain the speed of traffic!