My 1996 6.5 TD Suburban 2500 ran fine when I parked it...next morning it turned over fine but wouldn't start. Got a fairly detailed fuel system troubleshooting guide online and went to work. Confirmed that fuel made it to the injector pump, but not to the injectors. Got most of the way through the troubleshooting process (just the PMD and IP left) when the motor seized hard while turning over with the starter. No warning, just "clunk". Any thoughts? Is there something in the IP coupling that could fail and cause this? Thanks!