Basically the Jeep overheats slowly when sitting idle and driving. I noticed the radiator fan comes on. The radiator is 2yrs old and I just replaced the water pump. I was thinking about going after the thermostat next?? The belt looks to be in good shape so I don't think its slipping.

I guess I'm looking for ways to better diagnose the issue without throwing parts at it. Can anyone help..

try cleaning out the fins for the Radiator and A/C Condensor, blow compressed air through them from the engine compartment.

Replacing the t-stat is a good idea.

T-stat = Thermostat