Ram TRX throwing code P2096

Sorry if this is too long, but I wanted to provide as many details as possible.

2023 RAM TRX, 6.2L supercharged V8. I just purchased the vehicle used a week ago, it has aftermarket long tube headers, and AFE air intake, and some sort of aftermarket exhaust. The exhaust tips say BORLA on them, but I'm not so sure it's a Borla. I am not sure if the vehicle is tuned, and I cannot tell. It feels powerful but no more powerful than what a TRX should feel like.

I have filled it several times with 93 octane fuel, and I have driven it approx. 500 miles in the last week without any issue.

I don't know much about exhausts, but this is what I can see so far: long tube headers was mentioned before I bought it. Headers on each side (4 tubes) weld into what looks like a 4 to 1 metal pipe, and this pipe is immediately clamped to a steel pipe. This pipe leads into a GESI catalytic converter, which I am assuming is aftermarket. From there, there is a short steel pipe which bolts into another steel pipe ("bolts into" as in there should be a gasket between them, and its shaped like diamond like <>). This pipe leads to an X pipe, which I also believe is aftermarket (I think the stock resonators were here). From there, it later leads into the stock muffler (part number confirms it). However, the muffler looks to have been removed and welded back on...a friend of mine suspects the mufflers were cleared/hollowed out to make it louder. Then it leads to the exhaust tips.

It was really dark out and I could not see where the O2 sensors were located, but I will check again in the morning.

The exhaust is extremely loud; I have never heard something so loud in any street legal vehicle before. Every day I get comments on how loud it is, particularly at WOT. Remote starting in the cold in my backyard sounds like a helicopter landing. I have set off other car alarms before by remote starting it.

The code I'm getting is "P2096 Downstream Fuel Trim System 1 Lean". I cleared the code, and within 15 miles of driving, it came back. The temperatures have been approx. -2C/28F. What I have researched is that the downstream (post cat) O2 sensor is detecting a lean mixture, but I am not 100% sure. From what I can tell, the problem is:

  1. Catalytic converter is not doing what it should be doing
  2. Leak somewhere between the engine block to the headers and the O2 sensor downstream of the catalytic converter
  3. A failed O2 sensor (doubtful, doesn't it throw a different error if the O2 sensor is bad?)

Again, drove 500 miles without issue. Now I have cleared the code and it comes back after driving 10-15 miles.

I will bring it into the dealership next week, but I've been told they may decide to charge me for the diagnostic since some parts are aftermarket (i.e., those components no longer have a warranty since they are aftermarket), so I'd like to have an idea before I bring it in. Is there anything else it could be? What would a potential solution look like?

TLDR: 2023 Ram TRX, aftermarket headers, exhaust, intake, aftermarket cats, code P2096 Downstream Fuel Trim System 1 Lean.

Edit: no power loss, once engine is warm, no rough idle at all. Maybe a tiny bit of rough idle when it's cold but I've only driven it a couple times with this code on, so not enough to say...