I have seen a few cases of electrolysis in the 4.0 eat the impeller on the water pump and cause similar symptoms. The worst was barely out of warranty when it finally quit blowing hot air. You can test this by removing a heater hose from the core and starting the engine. Coolant should flow out rapidly from either the hose or the core depending on which hose you remove. If it doesn't the water pump isn't pumping any water.
2012 Silver Sport S, Silver, 6 speed, soft top, 3.73s, LSD, PCG, Infiniti, deep tint windows, Pro Comp 1028 wheels, 33" Duratracs, Smittybilt bumpers and steps, KC fog lights, Mopar slush mats and fuel door.
Happiness is a belt fed weapon.