Another silly question, have you inspected all clamps, elbows, piping and welds from your cold side? I have heard a few issues in the past of:
COBB charge pipe cracked weld on support bracket.
Couplers blown off due to clamps loose after a tune.
Welds cracked on support flanges for intercoolers.
All of these scenarios would give you reduced boost, a loud hissing sound and may not throw a code. After everything else and now this last bit of advice, I am at a loss. Good luck to you! Let us know what you find.