yeah something is definately not right.
First off, what car/year do you have?
What are you checking boost with AP, gauge, ecuexplorer, etc.? AP would likely be the most accurate.
Have you checked for any vaccum leaks or holes in your intake system?
May want to try the hwg duty map and see if that helps any, but if your down about 5 psi I dont think it will help.
May want to try the 91 oct map, or if you live in california the cali map.
Check the adjustment on the wastegate actuator arm. Search for intsructions on it, basiclly take the c-clip off and put a little preload on the wastegate. It helped me hit target boost when I was about 1 psi low. But then again if your 5 psi low and were hitting stock target boost probably not the problem.
And of course, if you can put the stock bpv and airbox on.