JO-JO

I recently brought my car out from storage and after driving it i notice that on the boost gauge it will not build boost until very high RPM's (3800-4000) and when it does it is only reading 3-5psi and it doesn't seem to hold the pressure at WOT the car has a full 3" turbo back exhaust big flow cats and mufflers, and the turbo was upgraded to a 19T any thoughts would be great,