Does anyone know of PCM (entertainment/nav/etc) problems with 997.2?

Since new in 2010, my unit has always had glitches (temporarily shutting off, then coming back on). I've questioned this repeatedly when the car was serviced ( in Fort Collins, Monterey and Beverly Hills). The service people run a diagnostic scan and see nothing wrong. I drive away and it happens again, as always, same day.

This week, the unit stopped working completely during an otherwise nominal drive. As in the past, the unit shut off and "recycled." But this time, it simply came back to a white screen (which goes black intermittently- then back to white screen).

At Monterey CA in 2011, I was told that the 997.2's main computer gets so overloaded that non-essential functions like PCM get shut off temporarily. I don't have bluetooth, no phone- just XM radio, navigation and CD. I don't like owning a new six figure car that - from the beginning- has no reliable radio and navigation function. What really bugs me is that the car's computer diagnostics don't see an ongoing problem...and I'm stuck with nothing working after mentioning it every time I've gone to service at three dealerships.