rbertels,
What your describing is identical to a problem I had with my Carrera. I finally had it fix when my wife took the car with her best friend to go shopping. Well, it came no surprise to me when they called up and said the car was dead. My wife's friend got out and pushed the car off the road. When they left, she was wearing some pretty tight fitting jeans.
I would have paid money to see her pushing from behind. Well, an unknown person in a 930 pulled to the side and helped them with getting the car into a parking lot. The guy mentioned to my wife, you sometimes got to push these things..My wife said no one would stop to help them. Figures a brother in another Porsche would be a hero..Thanks to whoever that was !!!
I updated the head temp sensor and DME and have not had a problem since. I also notice since doing that the druck pressure gauge seems to be working better too..
Good luck !!
Pat