Engine overheats unless at highway speeds

So, my car overheats almost randomly. I had since replaced the water pump, thermostat, main hoses, as well as done 10+ reverse and regular flow, system flushes. My radiator is only a year old, and the fans were replaced at the same time and work properly. Yet when I’m idling my temperatures will go from 80 to 230 in 1-2 minutes and will stay there until I get up to highway speeds. Some days it will go all day without overheating even though it’s rare. I can’t for the life of me figure out what’s wrong with it. The only other thing I can think of is the heater core since my heat doesn’t work at all and when I try and use the heater it causes the car to overheat immediately. I’ve been trying to figure this problem out for the last year. I’ve also done comprehension tests and head gaskets seem okay as well as I haven’t had any coolant getting into the oil at all. I’m at a loss and would like to stop just throwing money at it hoping it works.