Dear Tony, thank you for your ideas!
0 - I have a 4.0 liter 6-cyl automatic 2000 US Sport with air conditioner (including the heavy duty electricals group)
1 - I just showed my Jeep to the dealer. They have no idea so will change everything (rad, pump, thermostat)
2 - may I ask you
(or perhaps somebody reading this) a favour
after driving and shutting the engine touch your radiator with a palm from the fan (engine) side
Is it evenly hot on the driver side and the passenger side? Mine is much colder on the driver half. There is an invisible vertical line somewhere in the middle dividing the hot and the cold parts of the same radiator core. But it seems to be all filled up and coolant draining into the expansion cup.
3 - I noticed this JK Wrang post:
JK Interstate Driving and Overheating
but I can't post a reply there (not enough permission - ??)
Somebody please tell that person to touch the rad with a palm like I said.