[CDG]

OK, I just spoke to mechanic after talking with jsvxstyle.
As per J, I checked on the universal O2 sensors he installed and he said sortof:
He initially installed the NGK universal 3 wire O2 sensors. then ran the onboard sensor diags on the Suby, as you mentioned, and they failed. so he took out the NGKs and looked for the factory ones, nothing around(now there's a surprise) so looked for other, what he actually ended up installing were 2 Bosch Universal 3 wire O2 sensors, ran the sensor diag, and it came out clean.
So, I'm not sure if I should really worry too much about the sensors now and focus on my real issue.
Which as you mentioned:
1.Check the EGR valve.(left out detailed description)
2.Check PCV.(left out detailed description)
3.Check those intake bolts?? I know where it is.(left out detailed description)
4.then measure differential temps before and after Cats. to confirm if my Cats are toast.

Or, imagine my mechanic is good at WAGs and try some Cats just to see how lucky he is.
I am allowed to buy time to fix this problem, so I have another 3 months to try some other things.

Thanks to jsvxstyle for the 1.5 hrs of your time last night. You obviously know your ****, and I want to thank you for your help so far, and let you know that I will be talking to you shortly. After I look at 1,2 and 3.