2012 ISX 12 CM2250 - rough under throttle

[tree98]

So when the rail pressure was at 29k did you shut the engine down and see how fast it would leak off? What you want is less than a 4000 psi drop in 1 minute.
If it falls off quicker than that, you start capping injectors and running the test again. If the leakdown rate improves, you know the injector you capped off is bad.
Maybe you have an injector or 2 hanging open? You say they were replaced 200k ago, do you know if they were replaced with factory cummins or some ebay junk?
Is the engine making oil?

I forgot to mention, you need to open a separate data monitor window in insite to watch the rail pressure.