1999 Jeep Grand Cherokee Problem

Idle prolem could be a dirty throttle body or sticky air idle control motor.
If the Jeep is a 6 cly. the adjustment for the belt is the power steering pump.
If the Jeep is an 8 cyl. the tensioner is on the pass. side of car.

I have a 99' Grand Jeep Cheerokee Laredo 8 cyliner all time 4 wheel drive that has an idle problem. The idle gets up to 2k rpm in park, neutral or drive. It also idles as low as 200 rpm to nearly dying when I come to a stop. Ive had the IAC motor replaced twice with factory parts with 0 improvement. Ive been told the computer module needed to "accept" the new part in order for the idling to adjust appropriately. And that by driving the vehicle and / or manually adjusting the module, would fix it which niether has worked.
The problem seems to be increasing and not getting better. Any advice.
Note: The problem seems to happen at long distance trips over 65 miles hour at 20 minutes or longer.
Problem: Extreme High or Low idling.