2011 Buick Enclave possibly running rich.

I have been trying for a few months to repair my Wifes 2011 buick enclave CXL with the 3.6 V6. I have already changed the timing chain which was unrelated to this problem but did fix the cam crank correlation code it had. I have a P2099 code. i have watched the MV reading on bank 2 sensor 2 and it basically always stays at 500Mv or so. it does go lean when the upstream o2 goes lean during decel fuel cutoff so it appears to be functioning. the bank 2 upstream o2 is switching and going between 800 and 0 as I would expect. i tried to verify it is working by holding the throttle around 2500 RPM and then letting off suddenly and in decel it drops to 0 but then right after that it seems to jump rich and stick rich for a while. bank one does not do this it goes straight back to switching after the decel fuel cutoff. the odd thing to me is fuel trims seem to be okay. they are at the worst ive seen averaging -7 on bank 2 between long term and short term. this problem seems to be worse when the engine is cold and on cold startup it wreaks of fuel but seems to clear up after 10 or 15 minutes. It also has a evap purge code which i have already diagnosed as a urge solenoid issue and will be getting repaired. I will attach some pictures I took of my scan tool showing the o2 sensor graphs. sorry if they are hard to see. I don't have a memory card for my solus so I can't save images as far as I know.

As seen in the pictures I attached the rear sensors do oscillate a little bit which I attribute to old cats that probably aren't as efficient as they used to be. bank 2 sensor 2 does not go full rich even at full throttle. I have not tried adding another source of fuel such as propane or anything, but I can try if needed. I have a P0496 for the purge valve which I thought could cause some of the issue but kind of figured it would lead to negative fuel trim numbers on both banks. It does not have any stalling issues at all after filling up. only other abnormal issue I notice is extremely poor fuel economy and if you start it, then shut it off then restart it, it has an uneven crank and almost can't turn over like it's getting hydro locked. I have not pulled the spark plugs yet but will do that tomorrow. a can't easily pull bank ones plugs because they are under the intake on this engine. it does not have a normal vacuum actuated fuel pressure regulator. this is a direct injection engine and I believe the regulator is part of the high-pressure pump.

Any exhaust leak before the downstream o2 will set this dtc.

I have the same code. Did you ever find a solution? I read somebody suggesting swapping the O2 sensors on both downstreams to see if it switches to the other side to help eliminate whether it's the O2 sensor.

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