I would try either flushing the radiator with Muriatic acid or buy a new one. The acid is a cheap try though and can work if it's a minor blockage. There's nothing like a new radiator though.
But, a friend and myself just went through the same problem and it was internal
Kepp a close eye on your oil and coolant levels and check for oil and coolant mixing often.
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Too much to list. Best ET on the car so far with stock 2.73 gears - 13.73@102mph
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