2019 Cummins x15 Slow no power on hills !!

That's about right on the boost. Unless you turn off some settings they are normally programed for fuel economy.

 

Their is a engine repair place here in the States called Pittsburgh Power. The build high power Cummins engine and others. They can tune the ECM and and change settings so it run better then stock. They also seem to know a lot about how the engine works. They fix the problems thedealer can't fix. Because the know how the engine should work with all the computers. Obviously you can't get your truck to their shop, but the do answer questions on a live radio show every week on for 2 hours. You could call and ask them for free. They are pretty high tech shop. They are doing remote ECM tunes in the states over the internet with shops they setup with laptop computers. So drivers don't have to send their ECM to them anymore of they don't want to. Then even repair ECM. If nobody else here has answer you can try calling their shop or the free radio shop they do everything Tuesday 12pm-2pm eastern time here in the States. You can look at their website and see if they might be work calling.
Pittsburgh Power - Diesel Truck Parts, Service, and Repairs

Their is another guy on YouTube who seems to know lots about the ISX he might be able to help. He rebuilt his ISX engine himself and put all the videos on YouTube and talks about the sensor going bad

 

Rawze knows his red engines but don't know if he's still active