Swapped back to my Stage 2 tune and the exact same thing is happening.
If I don't touch the gas, this is exactly what happens:
Turn the key to "On", gauges sweep and all necessary lights come on.
When I crank it over it has that typical rev like startup. Fires up to 1200-1500 then starts to drop back down.
If you notice, when you start your car, it take the gauges a few sec to "catch up". After that initial rev up the gauges catch up right around the time the idle settles in. It's at this point, the car shuts down.
I turn key.
Car revs up to 1200.
Then shuts off.
If I work at it, I can keep in on for a few additional secs by giving it gas. I can't keep it longer than maybe 5 secs.