I would try replacing the 2 vacuum lines at top front of engine first. This is quick and easy to do. Here is the post (vacuum line fix - low boost, underboost, 30ff, wastegate rattle)
I told my SA and he thanked me. He said this fix has solved some recent intermitant problems on cars with over 40,000 mile.
I did it my self at a cost of $7.00 for the vacuum line.
Hemostats (Medical scissor like pliers)work best to remove old lines and install new ones. Im changing all others vacuum lines soon.
My car runs perfect my tuner is going back on soon now that i know this was the problem. Right now my boost will max out at 9.2 psi 0n 91 oct.