I have insulated garage doors, insulated ceiling and insulated attic steps but I don’t believe that helps much to keep the garage cool because it still gets hot as hell in there. Warm air rises. You could leave the access door to your garage attic proped open or cut a hole in it and cover it with a screen to let some hot air go up. I guess it should exit thru the ridge vents or gable ends? I have a solar powered attic exhaust fan in the roof to try to get the air flowing from my soffits thru the roof. I think I will have a Mitsubishi heat pump/dehumidifier installed. It costs about $6K.