Reread your description and you got a screach even when you capped the PCV valve. That tells me your getting manifold vacuum to the crankcase somewhere besides the PCV valve. With the PCV capped there is no vacuum to crankcase and it shouldn't have screeched even with the TB gasket.
I have already fixed the pcv screeching issue. The only issue I have left is bad fuel mileage. Averaging 13 to 14 mpg