Diesel particulate filter

Thank you all, after further investigation by the shop it turned out to be the crank case breather was clogged and wasn't letting the DPF regenerate. Replaced and cleared codes and down the road for the low low price of $850! I State Truck Center in Livingston MT. Good work by them!

If you can't find one, just have a muffler shop remove it and weld up a replacement straight pipe......

My son had one replaced at Cummins in Jacksonville, Fl, under warranty. If I recall correctly, they said it was a $2,600.00 replacement if it wasn't covered.

I would contact these folks... might have an installer in Billings.
https://www.dieselspec.com/

I'm not sure what you need but, Dales Super Store has several DPF's listed. Maybe you can find what you need and get an idea of the cost.
I've never dealt with them.