One day Im boosting fine, 12-10-12 pattern. The next day I see 11-8-6. I had boost problems before but it was about 4 years ago so I had to dig up all my troubleshooting info. I spent an 8 hour day going through every link of my secoundary boost system. Everything checked out, vac holding vac and pressure holding pressure. At the end of the day I took the car out for a test drive and still only reached 6lbs on secoundary, however, this time I could here a faint whistle noise different then ive ever heard. I got worried that maybe I had a problem with the turbo itself. I decided that before I started taking turbos apart I would check one last thing, The mid cat. For some reason I thought this was highly unlikely, my problem had to be more then a cloged cat. After removing the cat I could hear and feel what seemed like loose rocks rattling inside. Apon Tipping it up and bangging it allittle large chuncks of the catalyst came out. I had found my problem. I cut the cat open, removed all the guts and welded it back up. The next test drive was awesome, boost was back (I had to turn it down alittle) and the car sounded great.
All the info on the web I found said that boost problems caused by a deteriorated cat would be seen gradual, Mine was not.
My mods are intake, pullies, downpipe, cat back, Pettit computer, and boost controlled by daws(sp?) devices.
mike

 

Same thing with mine.