Jeep overheating

Suspect thermostat problem have tried replacing?

Thanks Docfixit. That's where I will start. It just seemed strange to have the heat get hot and then cold. I was suspecting the heater core but I didn't think the heater core would cause the overheating problem. The water pump isn't leaking and sounds fine. The coolant level in the radiator is fine also. I have been having issues with the heat not getting hot and thought the heater core was clooged. Would a clogged heater core cause an overheating issue?

Heater core would not effect engine cooling. if core blocked would be cool all the time