regulate the speed. I can feel the go pedal going down when Cruise is engaged if it need to pick up speed, but does this device simply throttle off (when going downhill for example), or is there a more technical approach to it? E.g. reduced fuel?

 

It's strictly a servo that operates the throttle in lieu of your right foot. No changes in spark advance nor fuel trim based solely on the cruise setting. Indirectly, of course, the ECM will adjust spark and fuel based on the TPS and VSS, but not directy from any cruise inputs - it's no different than if you throttled with your foot.