Truck was never abused or driven hard. Always had regular oil changes and check-ups. While driving to work one day, the engine lost all power and came to a stop in a live lane. Had the truck towed to a shop where they did a diagnostic test and halfway through the test there was a loud bang and the engine stalled again. When we removed the right head, we could see that one of the valve stems had snapped at the keeper and the valve spring snapped in half. After replacing the valve and spring the truck was still running rough and wouldn't stay idling. After a crap load of tests and new parts, it turned out that the camshaft position sensor and crankshaft position sensor needed to be replaced.