2006 3.0L fluctuating temperature issue

So I've had my Suby for a while now and it temperature has been fluctuating from normal to getting close to overheating, specifically when idle. I've changed the thermostat twice now, just did the radiator as a mechanic said it probably was too old and had another look at the water pump and they said it looked okay. So since I've done the thermo and radiator all it can be imo is the pump. I am just worried if it's not the pump then what could it be? I've done the basic tests to make sure it's not a gasket leak but it can't be 100% ruled out. Has anyone had this issue and solved it? And advice is appreciated.