Would you believe it was the MAP sensor causing the problem all along and there were no fault codes to indicate such?
I now have 3 OBDII readers and a temperature gun in the stock pile, the first two OBDII readers would not link up to the computer. I accidentally found/purchased the third reader and it confirmed the overheating.
For the meanness of it I replaced the MAP sensor and after a week of driving and a tank of gas the gauge never got over 205°.

And yes I realize this thread is over a year old.
I've been fighting this thing since August 2012!
And FERM the fan would come on at 221.9°, so you were dead on the money!

Glad you were finally able to fix it...if you are like me, stuff like that can drive you crazy until you figure it out.

Congrats Tsubaki.. It's been a long hard fight I'm sure. Glad you came out the winner. Now it's miller time!! :happy:

MAP sensor? Was it running rich or lean? it doesn't make sense to me, but whatever works

Jeeps run lean to begin with for emissions reasons. If the MAP was far enough off it can push stoic up to around 15.5-16:1 which would lean it out big time. Never heard of one doing it at idle unless for some reason it wasn't going into closed loop.

I actually argued with my father that it was not possible to be the problem. His response was "you done replaced everything else, it's going to be a lot easier changing it instead of replacing the head gasket or timing chain".
The live data stream from the code reader showed the timing jumping all over the place after it got warmed up, I was convinced the timing chain was stretched slightly.
Glad I was wrong and did like Daddy said.

The timing chain would have no effect on the timing. The timing is based off of the crank sensor, and only uses the sensor in the distributor as a sync signal to tell it when it is at TDC on #1 for fuel injection.

Slightly off topic, but Tsubaki I have a 1997 Grand Cherokee my brother in law and I are gonna be parting out if you need any parts. 4.0 engine, 4x4, automatic, black exterior.

Thanks bradford, those parts are getting scarce and should command a premium.