I see in another thread Poseidon215 has the exact same problem with his 05. Whatever this is, it seems unique to 05's.

UPDATE: - It doesn't appear to be the MAP sensor. Disconnected it last weekend, and it's had three incidents since then.

Has anyone with the problem had their PCM flashed by GM? There are a lot of updates since 05... I'm half toying with the idea of an Overkill PCM to see if that fixes it.