On the 480CE installed in the 2005 460, there is an issue called stall/stumble. On the boat I owned, it only reared it's head when starting a fully warmed engine. It would start then immediately die. On the second start attempt all was fine. I never had it die after a successful start. The fix was to have Cummins update the ECM. No problems after that. The ECM controlled 480CE idled fine at the set 600 as well as the slow idle of 550.