Many questions

[JimT]

check the flex pipe (exhaust bellows) that comes after the turbo. Not sure about your peete, but my pete (2012 587) has it situated only an inch or so away from the frame rail and they are known to go bad after a while. I didn't notice mine leaking until I was running a parked regen and saw the slightest wisp of exhaust gas escape.

How is the rest of the engine performing? You mentioned potential exhaust issues, but nothing else. Also, you didn't mention if the truck's been demandated. I'm guessing from your description that it is not, but need to know for certain. What's your oil and coolant consumption look like?