where did u hook your guage u to at?
also
u should be able to get 15 easily, cuz thats the factory setting.
its possible one of your wastegate hoses/ lines could be dry rotted or leaking, inspect them, heck buy some hoses, and replace uhm if they look Old.
make sure to take them off 1 by 1
you dont wanna mix up boost lines and vacuum lines
could possibly be a bad wastegate selenoid / switch
you could aslo try bypassing the Wastegate selenoid switch all together and see if u get more then 10 psi .
but be careful not to floor it cuz if this is your problem , you will hit some MAJOR boost
and tomorrow you will me making a Thread, called
"how to replace head gaskets" haha
do you run a cat converter on your car? it could be plugged, restricting exhaust flow, killin yer boost as well
im just giving ya some ideas to try
could be any or maybe all of those
