05 Yukon overheating at highway speed and heater won't heat
The fact that both the cabin heat and the engine overheating I believe is a sign that your thermostat is bad. The thermostat is a mechanical valve that runs in-line of the coolant pipe between the engine and the radiator. When the coolant gets up to the optimum temperature, the valve pops open and allows the coolant to circulate. I think that is your issue.
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