It's hard to believe it could be something mechanical that would shut the car down. Has to be in the tune somewhere that is shutting it down when it reaches a certain psi, or knock, or timing map, etc. I know you've checked the tune over and over again, but what mechanically could do what you're describing?
Is it shutting down completely, or is it acting like it's blowing the spark because of bad coils or to big a gap on your plugs?