Any smog experts out there?

Don’t discount the new cat being bad. Even with only 3800 miles since replaced. The cats are very responsible for lowering nox. If you can read live data look at the switching rates of the pre cat o2s and post cat o2s and this should tell you the cat is working or not. The front o2s should switch fast and the rear 02s should be fairly consistent, the fronts should switch between 0.1-0.9 volts fairly quick, and the rear should be pretty steady at 500-700mv. This will tell you the cats are working.