Cummins ISM not reading boost correctly?

[Waterloo]

That is low miles, the pyro is at the edge, so you may just have a head gasket issue... I would lean towards a bad gasket, OR you have a stretched or lose head bolt. I would pop the top and check the torque of the bolts holding the head to the block. If one has worked its way lose, and this has been an issue on the ISX, you may get lucky. I would go there first, re torque the head bolts. I do not know the torque specs, but that should be easy info to get. I think you dodged a bullet here. ;-)

Side note, the head bolts are one time use, as they stretch. If it is a lose head bolt, I would replace and if me, pull the head, replace the gasket and install new bolts. Not a huge job, if you have a way to pull the head, they are not light.