Computer wont let it get boost in park. Try unplugging the lower vacuum line on the BBV and plugging the vacuum line. Leave the lower BBV nipple open(closest to rod). Engine not running the BBV should be shut, as soon as you start it should open, rev it at the throttle body cable and you should see the valve snap shut. Still should not build boost in park. Take for test ride and see if it makes a difference in boost.
BBV vacuum actuator could have a hole in it. My original BBC actuator had a tare when i looked up where the rod was coming out.
