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Hi. Those engines do have some issues with the cylinder head temp sensor causing the gauge to spike. But if coolant was coming out of the overflow, then I would not suspect an electrical concern. Your engine overheated so I would suspect the cooling system.
That could have been a coincidence from an air pocket. I can not see any relation with the cht sensor and going from park to neutral. Especially if it overflowed before. Have you verified the coolant level? If there is an air pocket or low coolant the gauge will act erratically.
I think you need to verify the coolant level and redrive it. If the gauge starts to read high again, go check and see if you can verify if the engine is actually overheating. Which you did say has already happened. This just may be a bad t-stat then air pocket.