Assuming the differential pressure sensor is good, and there are no leaks, you may indeed be up against a DPF replacement. Sadly, bunches of these that were perfectly fine get tossed in the scrapper due to the silly added (unnecessary) phase of the Gen3 Dieselgate nonsense.
Couple things I'd do:
Get to the hoses for the G450 and G505 pressure sensors on top of the engine, the ones on a bracket under a little space blanket. Carefully remove the little hoses that go to them, and with compressed air, blow back down the tubes, to make sure they are clear. Also make sure there is no soot up in them, and that the sensors' nipples inside where the hoses connect are clean. If there is a buildup of soot or moisture in them, they cannot get the correct reading. One is for the EGR, one is for the DPF, but they both share the one tube.
If that all looks good and clean and secure, then you can initiate a manual regen provided the ash load is not too much. Not sure what the threshold is on the CRUA, but it won't allow one past a certain amount. This does a super powerful regen that can sometimes overcome a DPF that is not performing as well as it should due to a variety of things, but often driving conditions. You may not fall into that, though. This is for folks who let the engine idle more than necessary and do lots of short trips with sometimes interrupted/incompleted regens.
The DPF itself is a big deal, as it is well over a grand and it is labor intensive to replace. It could be around $3k to have it done.