Where is your PCV connected. When under heavy load the pcv will not be doing much due to a lack of vacuum. This could cause crank case pressure to build and blow out oil. When you loose pcv vacuum is you have a weak seal combined with excessive increased crank case pressure it could blow out. You need to figure out where it is coming out to start with. My guess is the front of the intake. Did you use RTV on the intake ends or the gaskets. The gaskets don't seal. At higher rpm you will also have a lot of oil flowing in the lifter valley which could contribute to intake leaks.
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