So the engine block, the water pump, thermostat, and pcm have been replaced. Works fine except: at high speed engine temperature is good. At low speed or idle it heats up rapidly to just above half-way and stabilizes. Then the low coolant warning like starts to flash and comes on permanently. Driving at high speed reverses the process. The radiator fans are working, and the coolant is in the radiator - it gets hot to touch.
Is the radiator full and all the air out? That’s the question. You need to make sure the radiator is actually full with no air pockets. Hot to the touch is not the way to check for coolant.
This definitely sounds like air in the coolant system. If you have the 3.8L, which most Intrigues had, there is a bleeder valve on top of the thermostat housing. You need to open that valve (engine completely cool, of course) before filling the engine with coolant. When coolant starts to come out of the bleeder, let it flow for a few seconds, then close it off, tighten, and finish topping off the coolant. Hopefully, no damage was done by operating the vehicle this way and your problems will be solved.