Kevin O'brien writes:
..mine overheats mostly when going
uphill...but also get finicky...blows cold with heat
on, then hot...red light flashes...stops flashing.

I once had a problem like this with random overheating, with the same
symptom of the  heater going cold when the engine temperature began
rising.  I reasoned that the  cause must be that something was causing
the circulation from the engine to the radiator to stop.  The cause
turned out to be a water pump impeller that sometimes spun on its
shaft.  Replacing the pump cured the problem.

Chuck Hill