C15 down on power!

My truck has been running like it has a 4cyl in it. When loaded I drop down to 40mph or so. It’s drastically down on power.
I had a guy hook a computer up to it. He said it’s not reading boost and there’s a barometric code being thrown. He disconnected the boost sensor and then got a code for it, so he feels that sensor is working. Do you all have any suggestions on where to start to solve this issue? Is there a barometric sensor on the motor that could be bad that’s causing it to de-rate….would that do it? Could the boost sensor be bad even though it doesn’t throw a code for it when connected?
Please and thanks for your help.
Cat 15 3406e 1LW

 

When it fails does it cause this issue?

 

It doesn’t sound crazy…that’s been suggested, but these are fairly new. Like less than 2000 miles.

 

I won’t rule that out. I’ll replace them along with the two sensors. 1 of the 4 hopefully solves the issue.