My car is a 93SSEi with 116K miles. It always runs a little hot. Normally around 210, but 220 on hot days or slow traffic. However, when climbing hills at lower speeds, like 2 lane mountain roads it overheats quite quickly.

Yesterday we were in Idyllwild at around 6000 feet and just drove 15 minutes to the upper end of town, a 600 foot elevation increase, and it almost got into the red. Travel speed was low, 25-30 mph. When that happens it won't restart until it has cooled off for 30-45 minutes.

Coolant level was good. Both fans were running when we stopped

It sounds like you might have a radiator that is plugged or a water pump issue. Flush the cooling system and verify that the water pump is moving water. Then refill with fresh green coolant and see what happens.

Defiantly a good place to start also while doing this wouldn't hurt to throw in a new thermostat. 180 might be up your ally if you do alot of hill driving. Also check to see if the fins on your radiator is not crushed.
Going up hills puts the most load on engine. Idk what the hill climbing RPM'* on bonnes are ( I live on the coast not too many hills) but alot of things come into play. Higher the RPMS water pump does run faster but running higher rpm'* make it heat up faster. Lower RPM'* slower water pump speed and lower RPM'* high loads is bad for a gasoline engine. knock and stuff like that.
In conclusion change the fluid, thermostat and check the water pump and go from there. if anyone knows anymore on my second paragraph you can rip me apart if I'm totally wrong.