06 TL performance issue

So, I've owned an 06 accord(j30) v6 6mt and now own an 06 TL(j32) 6mt for the past year and some change or 74k miles. I've always owned acuras and hondas and am having an issue with my TL. I know a fair amount about the mechanics and systems in place in these engines but am having a tough time with this issue. My TL... I bought this vehicle at 200k and it has run like a top up to 270k. Recently I've had a lack of throttle response/performance. The vehicle has thrown a cel for catalyst efficiency below threshold and a code for the bank 1 upstream sensor, however, the vehicle has not thrown a cel consistently and the cel comes on, then goes off on it's own. Currently it will not throw a cell, and I drive it from 9am to 5pm every day. But the performance is subpar most definately. It takes alot of gas pedal to get it moving and even then it does not move as the TL normally moves. I've checked the exhaust system for restrictions but nothing seems to be clogged or restricting. Have changed the firewall side cat, disconnected the 3rd cat and drove it with no changes, so it's not the cat, resonator, mufflers, etc. Replaced the PCV valve, no effect. Oh, and I just took it to the most reliable mechanic I know and they said it is running lean at idle, bit to bring it back once a CEL is thrown for further diagnostic. I'm at a loss. Some other info is the front(radiator) side valve cover gasket has been pushing oil out since the issue started. I thought there was excessive backpressure from the exhaust(maybe a cat) being restricted but that doesn't seem to he the case since I've replaced the read and removed the 3rd with no difference in performance. Thanks in advance for the knowledgeable input!

I've replace the bank 1 upstream 02 sensor as well as that(firewall) cat and no change.

Symptoms are the throttle response is sloppy as in, the vehicle runs "OK" up to 2700-3000rpm, but then studders and falls on its face above that.