I would look at putting in or trying to put in a good water pump driven fan and fan shroud. This really pulls the air through at slow vehicle speeds. Do an experimentplonk the bonnet up on your jeep feel the air displaced by the electric fans. Then go over to a friends car that has a big belt waterpump driven fan, you should detect quite a difference in airflow. The more air you can pull through a radiator the better job the radiator does of cooling the coolant.