First, Welcome to the TDR!
If you installed the plate, did you also install an EGT gauge? If you dont have enough boost at WOT, you will have very high EGTs which could damage something. (not to mention smoke like a mutha)
As for the 10psi boost with a #6 plate, you should have at least 20-25 psi if not more. Check the interconnector boots between the turbo output, intercooler, and intake of engine. (4 boots) The lower boots have a good habit of blowing off or splitting open. Take them off and clean with degreaser then alcohol to get em to stick. Also check the wastegate line coming off the compressor side of the turbo, could have a hole.
Now would be a good time to upgrade the air filter to a BHAF for more airflow. You can get a model #AH19037 at fleetguardfilters.com, and a turbo heatshield from fostertruck.com cant hurt either. .
good luck
-j