I am having the same issues i am getting an 02 sensor code aftet ive replaced both sensors with acdelco oem sensors. Car shifts hard in stop and go traffic but if i clear the code and readiness monitors it seems to go away for a little while and then the code comes back along with the hard shifting.

 

Check out your engine mounts (there are 2 dogbone style mounts on the top and 2 on the bottom) for cracking and degradation. In mine, the 2 on the bottom were still from the factory, so they were really bad and allowed the motor to move much more than it should. My theory is that this is what I'm feeling, but I haven't replaced the bottom mounts yet. I'll update when I do, though.

 

Yeah i ended up narrowing it down to the cat converter and secondary air injection system

 

I will take a look at those engine mounts tho

 

I literally have the same exact issue. After reading all of this, I will try ALL of the suggestions mentioned above. My 01 SS already has the new Cats, but I will change out the o2 sensors and (PCS) and (TPS) and the motor mounts. Thanks for everyone's information. Have a great day. Also, I will try to keep everyone posted via Update.