According to the mechanic who drove it in the mountains with a scan tool attached, said the engine is not actually getting hot, but the gauge does peg out. I've been around overheated engines and when I lifted the hood after it went into the limp home mode the engine did not seem abnormally hot. I wouldn't mind trying the aftermarket radiator, but if the engine is not getting hot, I'm not so sure that's going to fix my problem. To me it seems like an altitude change issue. Is there a sensor on this engine which measures altitude? Can that be faulty?
I normally drive at 1000 to 1500' altitude all day long with zero issues. Problem is only in the mountains.