[25stevem]

Once any vehicle is moving more then a steady 30 mph on the road having fans running to move air thru a radiator should not be needed.
Above speeds of 30 mph leaves these possibilities and possibly in concert with one another.

1) restricted air flow.
2) restricted water flow.
3) coolant moving thru the radiator too fast.
3) improper air to fuel ratio at certain throttle openings/ load conditions.
4) low cylinder pressure / retarded Cam timing)
5) retarded ignition timing, part throttle / cruse timing of less then 35 degrees with vacuum advance hooked up.
6) restricted exh.
7) excess internal engine friction.

If your not running vacuum advance, therein lie’s a good part of your issue!

Since you have a thermal gun I would take the car on another drive on a road where you can pull right off once the coolant temp gets to 220 and I would jump out pop the hood and with the gun see what temp the center exh ports are reading and report back here with that info.

I would first however remove the filter and cut it open to look for signs of trouble .

I have also seen two electric fans mounted right to the motor side face of a radiator create a nice airflow restriction above 40 mph.
There must be a minimum of 2.5” between the motor side rad face and the face of the electric fan(s).