As long as you are not hitting your brakes, then the answer to the OP’s question lies in which gear converts the gas pedal most efficiently into energy of motion for the vehicle… so, does a lower gear (going uphill) allow the engine to convert energy to the wheels more efficiently, or a higher gear (going downhill)?
My guess would be to try and be in a gear where the torque converter is most evenly matched when you use the gas pedal?
As far as cruise control… it’s goal is to keep a constant speed, not necessarily save you gas. Just sayin’.