Have you verified that the clutch fan is working properly? After 30+ years it may not be as efficient as when new. Also is your radiator 100% clean of sediment, and not partially clogged? In theory your fan should push cooler air from the engine compartment through the radiator to cool engine coolant. This is when you are driving at slow speeds and not enough outside air is forced through the radiator. Check the entire cooling system. It may be time to replace the clutch fan with an electric fan. If you mount it on the grill side of the radiator you'll draw in cooler outside air--except for this week where air temp here has been close to 90. Good luck!
If it has rollup windows and A/C it ain't a Jeep. It is a rebranded Dodge!