There is only one heater core, so the loss of heat to one side of the vehicle is not a plugged heater core. Now, if it does not overheat at highway speeds, that tells me (if the fans are turning on in traffic or stopped) a higher engine RPM is allowing enough coolant to flow.
I need you to review the 2CarPros' article below. It walks you through all the possible problems. Keep in mind, you have already done a lot. However, I think if you start at #5, it will be helpful. Review it and let me know what you find.
https://www.2carpros.com/articles/engine-overheating-or-running-hot
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Thursday, February 8th, 2018 AT 7:02 PM