Read this post and have very similar issues with my truck. 2020 6.6 3500 approx 27,000 miles. Noticed my truck was constantly reving up when thrown into park. I live near the coast in California cold Mornings are around 30f days are 60-70f.
After a few weeks of the truck reving up it finally stopped doing it as it was random. The other day coming up a steep grade it through an engine code P002. Took the truck to the dealer, the outcome: I need a new dpf. Of course part is on back order and expect it in 3 weeks. Read some threads about a module that controls the def fluid??? Not sure cause or reason my truck sees mostly freeway use.