I know that boost problems are normal and I have got one. I recently uprgraded the intercooler to an M2 Race and had the computer remapped for 13 pounds of boost. The third time I drove it hard I blew a vacum line. I was able to find the vacuum line when as I was replacing all the lines with silicon. After everything was put back together I drove it and everything was great. Boost was perfect. The next day when I went to drive it I have -4 boost and at 4500 you can feel the second turbo come on and the boost is -2. I have checked every vacuum line twice, the blow off vavles, pipe connections and I can't figure it out. I DO know that when I pull the line off the vacuum chamber there is no pressure (which is bad). There are no funny sounds during WOT. The only thing I can think of is that the primary turbo has had a bearing failure or the wasegate is bad. If there are any questions or answers please respond.

 

Have you checked the check valve going to the pressure chamber?

I'm sure your problems are worse then that but thats all I can tell you.