I know you didn't say it but does it have an aftermarket bov?? If so the piston in it may be stuck open. Had that happen when my car had a bov on it. Lived on a 2 mile dirt road and after a while all the dust caused it to stick. Big loss in power and a really loud air sound....major boost leak.
Cobb ap stage 2 ots, catless uppipe, catless turboback, Cobb Sf intake.