Just to be safe, I'd pull the valve cover and check to make sure the plug at the end of the rocker shaft is still there. On some older six engines this has been known to blow out under pressure, starving the valve train of oil, but still having enough resistance to get the light out after a few seconds when oil finally gets up the block's oil transport channel to the head where it begins building resistance after a few seconds. The remedy is to buy the newer design plug (couple of bucks) and drive it in. I also pinned mine to be sure. Bob H.