cut a story short i cant get my escort rs turbo to boost over 8-10psi ! ive tried 3 turbos and no difference at all ! just wont boost any higher!

anyone had this before or can think of whats causing this??

ive got an airtec front mount intercooler.
running cossie managment.

before i took the engine out i was running 28psi.
then i bought new turbo,intercooler and tubula manifold.

any ideas?????