Does it have an electric cooling fan / working properly?
When idling, open the hood and turn on the a/c, the fan should start. If not, check the fuse or voltage to the fan motor.
My next guess would be that the water pump impeller is worn.
to check fan operation turn ac on engine running the both fans should come on,if you have 3.4 engine you intake gasket might be leaking,or head gasket issue.use pressure tester and check for leak,also use block and hadgasket tester before you put more parts on it.the water pump on your car can only leak it will not fall apart or stop circulating coolant.