The Jeep service manual states the diesel may run hot at low speeds and to turn off the AC. What speed are you going? The clutch fan pulls limited air at low engine rpm's and the condenser is also transferring heat into the radiator. At higher speed under load it is usually more a function of cooling system capacity, if you checked the t-stat, radiator, water pump, radiator cap, etc., than you may need to upgrade the system. If your JK did not overheat before under the same conditions than you need to identify what changed.
Is there anything blocking the grille? Is gear ratio and tire size stock? Is the system building pressure and are you losing coolant?
You might think about upgrading the radiator and installing an auxiliary electric cooling fan for low speed driving with AC on. I find some of the aftermarket fan clutches do not work as well as OE. With an electric fan airflow through the core is no longer dependent on vehicle speed.
[CENTER]500 South Buffalo Drive, Las Vegas NV 89145 702-491-7710[/CENTER]