Cummins ISM not reading boost correctly?

[in2trux]

Scan gauge boost is electronically calculated, not actual.
Did you replace delta P (pressure differential sensor?)? The one with 2 tubes on the intake manifold.
Those tubes are notorious for clogging on the Isx and Ism. You can't clean the sensor, only replace.
It's a key sensor and can throw ecm function. Does it cough or sneeze? I don't know how else to describe it,
thats what it sounds like, very quick interruption in power. Some call it turbo cough.
I had that problem with the Ism I use to run, egr tune up cured it.

While your at it, exhuast gas pressure sensor should be replaced too.
They're about $80-90.
Other than that I would check for leaks in CAC that my be showing at high boost.