[gtroth]

I believe the tach will bounce when you crank it so next time it dies check that. That should
tell us the speed sensor is at least alive. You can I look at its signal and the ref signal at the dme connector on an oscilloscope. Tough measurement to make for the uninitiated, but if you are so inclined, that's a real good test.

Sudden stall sounds electrical to me. If it were mine, I'd want to rule out the ignition switch, dme relay socket connections, and any harnesses that might be shorting or loose connections (and grounds) thet might be resetting the dme.