Fair enough. I find it especially odd that it would go bad with no warning. And in my case, go bad and still run fine for 400 miles.
This is going to sound oddball, but could there be a massive exhaust restriction on a few cylinders so the backpressure is backfeeding into the combustion chamber? Or a seized valve? (I seriously hope not for your sake) Beyond that I'd think you'd need to look for a random electrical issue that is grounding somewhere unseen.