Cummins EGR valves are junk but all the ones I've changed (lost count by now) always set a code so I doubt it was that. Also, don't forget the basics, check all air to air connections, aftercooler for leaks. I haven't run into and low fuel pressure problems with these motors and we have a few with 8-900 thousand miles on them in the fleet.
Cummins Isx Fuel Shut Off Solenoid Problems