temp still dropping and downshifting after warm up .
 

I replaced the idle control sensor coolant temp sensor air flow sensor thermostat transmission fluid , and it still runs cold. even after a half hour of warming up as soon as I jump on the freeway it cools down and downshifts. I cannot drive it at night or early morning at all. I've read many threads and taken a lots of advice I'm still stuck witQh the same problem months later than a hundreds of dollars later. what is it ? Transmission ? Junk it and move on ? 91 4runner v6 auto 2wd.

Still sounds like thermostat if the engine is cooling below normal while moving.
There is also a temp sensor that signals the trans to allow OD, It is right next to the engine temp sensor.

Do you know what temp the coolant is actually ruining at?

It could be as simple as the thermostat is stuck open so the engine cannot maintain the proper operating temperature.