This P2096 code is thrown by the rear O2 sensor IIRC. I talked to a tuner and he said the code is usually thrown if your fuel trims (short and long term) are outside +/- 10. He said its more of a nuisance code than anything and the car should run fine. When the car thinks you are lean, it'll throw in more fuel to compensate so you will actually be running rich. Too Rich or Lean is bad, but Rich is always better and safer.
Since you are NA with light mods and untuned, why you are getting it perplexes me. You would need to have an exhaust leak around the rear O2 sensor for it to read lean. Your Tomei is just a catback so its way downstream of your O2 sensors, so a leak down there wouldn't affect your readings at all.
I've been getting the code as well; after reading your post, i'm far more modded than you. (Vortech, full exhaust)
I have never got the code until the weather started changing drastically. I'm not sure if you guys in NOLA are seeing 20-30 degree swings in temperatures like every other day but it has been like that the past 2 weeks here in Houston. I'll reset the ECU and the car runs fine and doesn't throw a code, then when the weather changes, boom, code thrown.
I'd try the following
+Fix the leak in your catback, probably should get it fixed regardless
+Pull your MAF sensor (it's on the airbox) and make sure its clean and not oily
+Take out your rear O2 sensor (not fun while attached to the car) and make sure its not fouled up.
+Check all your intake plumbing for leaks/cracks. Cracks in the intake hose could allow air to be sucked in after the MAF sensor takes a reading, which would actually make your car run lean.
I'm going to talk to my tuner and figure out what is going on with my car. I'll report back if I find anything. Hope that helps