Overheated, stalled, won't start till cool

First off, it's a 1996 Jeep XJ SE 4.0L Automatic with ~140k miles. Replaced thermostat and water pump before the issue below arose. I've been searching the internet relentlessly but haven't found the confirmation I'm looking for on my issue. Here's the abbreviated story:

Took a trip to the mountains and noticed the temp gauge getting close to the red. I believe one cause was that I was using overdrive and probably should have kept it in 3rd on the uphills. Anyways, I was coasting downhill when the engine cut off. Pulled to the side of the road and was unable to restart the engine for about 20-30 minutes. The temp gauge never rose back to the red, but the Jeep would still cut out intermittently and not restart until cool. I was able to drive to a gas station where I let it sit for about an hour and was able to get to my destination without any more stalls. The next day on the drive home it started happening again after a couple hours of driving through the mountains. The temp gauge never rose to the red but engine would still stall and not restart until cool. I noticed the underhood temps felt unusually high, and that the electric fan would not come on even when temps were above 220 (my A/C is inop).

From my research I learned that the crankshaft position sensor and ignition coil were prone to failure from heat, so I replaced both of them. I have been too nervous to take it on any trips because I don't want to get stranded or cause a catastrophic failure to the engine. I also learned about the Automatic Shutdown Relay, but did not see what causes it to activate. I am troubleshooting the electric fan and am considering hood vents to keep underhood temps in check.

My questions are:
1. Is there anything else I need to check to ensure road-worthiness?
2. Any recommendations for preventing issues in the future?
3. What triggers the Automatic Shutdown Relay to shutdown the engine?

Please let me know what other details I can provide.

Follow-up: I also noticed on the way home that while coasting downhill the engine would slowly rev up to about 1500 RPMs (IIRC) and then drop to idle repeatedly. It would do this the whole way downhill. Is this normal?

No, not normal. Suspect the Idle Air Controller.

One might suppose that the entire cooling system in due for some TLC, not just the thermostat and water pump.

Overheating can be caused by anything that decreases the cooling system’s ability to absorb, transport, and dissipate heat, such as a low coolant level, loss of coolant (through internal or external leaks), poor heat conductivity inside the engine because of accumulated mineral deposits in the water jackets or radiator, a defective thermostat that doesn’t open, poor airflow through the radiator, a slipping mechanical fan clutch, an inoperative electric cooling fan, a collapsed lower radiator hose, an eroded or loose water pump impeller or even a defective radiator cap.

The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. Any component part of the cooling system that is not fully doing its job will stress the others, and your engine will overheat. Temperature creep on the 4x4 trails, at idle, or in stop-n-go traffic, points to a weak or failing mechanical fan clutch or worn out water pump fins.

The most important maintenance item is to flush and refill the coolant periodically. Coolant should be replaced every 36,000 miles, or every two to three years. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat.

-Use a flushing/cleaning solution to remover mineral buildup or rust, and then drain and fill the radiator with a fresh 50/50 coolant and water mix. With neglected cooling system you may have to flush several times.

-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the thermostat with a STANT or Robertshaw 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out radiator cap will allow boil overs and/or allow the coolant flash over into to steam. You will see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.

If you have covered all the points listed above and still have overheating issues, inspect and test the head for cracks and head gasket for leaks. Exhaust gasses entering the coolant can raise the temperature of the coolant or cause steam pockets in the coolant that will temporarily block the flow of coolant

Read more about cooling systems here –


www.offroaders.com/tech/engine-overheating.htm

www.carparts.com/classroom/coolingsystem.htm

Thank you very much for the response!