Codes would be the first thing I would check for. I take it you have fuel pressure. Next would hook up the a scanner and watch PID for crank and cam, After that I would be looking at PID for injectors to see if they are firing and or duration time. (found a bad fuel pump by that engine was losing RPM and dying and Injector duration was going long, trying to get enough fuel).

Good luck.

Jason R. Gohn
Technician/Shop Foreman
Greene County Highway Department
Springfield, Missouri, USA