You may simply have bubbles in the cooling system.
A technique for bleeding the 4.0L is to get the rear of the truck higher than the front (facing down a driveway, put the rear up on stands, etc). Doesn't have to be much more than a few inches of difference, but the goal is to get the bubbles to gather at the rear of the engine block. Now loosen the temp sensor (located at the drivers side rear at the top of the head) just enough to let air escape. I'd advise doing all this with the engine off and cool (so when you fire it up and something goes wrong, you aren't showered with 260* coolant). Now have someone fire up the engine and wait until the air stops coming out. Tighten up the sensor and add more coolant. Eye protection is strongly advised. Full face shield is preferred.