If your sure you have all the air out, I can't see why you of all people can still have air in there. (Your not new to this), then my guess is HG or cracked head.
You say it only happens under high load, which = boost.
206,500miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
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