[bimmerboy]

boost tapering is pretty common on all cars with factory turbos.... my wrx had the same taper. It's usually more of a problem with the stock turbos being too small, therefore tapering in psi as the rpms increase towards redline.

If you upgraded to a larger turbo along with supporting modifications(intake/exhaust/fuel/ecu) you can eliminate this by keeping the psi constant once spooled...

Maybe someone can explain in more detail? i'm no expert.