Try changing you oil and if that does not help you will need to rebuild the tranny or replace it.
44re
It is bolted on the back of the engine.
Yes
Automatic transmission fluid.Automatic transmission fluid.
Yes. Transmission in park. Transfer case in neutral.
bad heater core.
it will fit but the electronics in it are different so no
Two sensors in the same part, yes.
The transmission does not have a drain plug. You have to remove the oil pan to drain.
Yes, pressure and return cooler lines.
No, the Grand is different from the Cherokee.
It is a three wire switch on the driver side of the transmission.