Cummins ISM not reading boost correctly?

[Waterloo]

Man, that sounds like a head issue... Been there... I would go get a block test kit from your local NAPA or auto parts store... Many guys poo poo these test kits, but it diagnosed mine in a matter of seconds. Not good, I nursed mine for a year, and then she was building so much pressure it blew out my radiator and my lines running to the Tri-Pac... The Tri-Pac episode was the end... She went in for the in frame a few weeks later. I think you are looking at a big bill here... If you have high miles, sounds like in frame time. If not, you may get away with a head replacement or just a new head gasket. If it is the head, just get a new OEM one, do not get a reman. I think you had a high heat episode, if you have an inline 5 reader and Insite, it will show up. If not, take it somewhere and pull up the ECM recordings to see. Sadly you need to be a mechanical engineer with these new trucks, as these shops are clueless.

You need a Pyro gauge if you do not have one...

I'm sorry to even have to tell you this, it sucks.

Rawze or one of the other guys will chime in with more info and other things to look at... Sad.