Valve broke off and jammed a piston or something. We still have some of the pieces of the valve. :P Took a while for the mechanic to figure out why the engine just stopped. We were driving to Disneyland, car pool lane on the 91, just starting to catch up to traffic, and the engines just dies. No sputter, maybe a quiet thud, but goes down to 0RPMs fairly quickly, and the truck coasted to a stop.
Escape will make me God.