2012 5.3 02 issue with Kooks Headers

[drew.brigham]

Just installed Kooks 1 7/8" lts with a 3" catted y pipe (also from kooks) on my girls 2012 silverado 5.3. Currently it is running open y pipe as I need to get an exhaust clamp to connect the y pipe to the corsa cat back. Getting catalyst inefficiency code. I have not yet changed my MAF calibration because I have heard I need to change some response time with my 02s as to account with the change in location of the 02s and the increase in size of the pipes. As of now the truck is running rich cruising on the highway (pulling anywhere from 15% to 5% fuel) and has random knock spikes (about 6 degrees)(knock sensors are bumped down 20%). Is there an 02 table I need to change to make the codes go away and help account for fueling before I chase my tail tuning the MAF? I attached the current tune in the truck along with the base read. 2012_Adrianne_Chevy_Silverado_5three_DODoff_35tires_knocksnsr_PE_tqbump_transtune3_iat_stocktimi.hpt 2012_Adrianne_Chevy_Silverado_5three_BaseRead.hpt

[5FDP]

Fix the rest of your exhaust before you start doing too much. Open y pipe could skew the rear o2 sensor readings.

[drew.brigham]

I was thinking that. But is there a table I need to scale to account for the increase in diameter and change in location of the front 02s for fueling? On a buddies 07 Tahoe with 243 heads and lts we changed a table for the 02s to account for the change but I cannot remember what we changed. Im about to make a tailpipe sniffer so I can dial in fueling at WOT but until then Im just wondering if thats only on older vehicles or if I'm crazy. At work I mostly tune hellcats and demons so Im a little rusty on the GM tuning.
Thank you for any advice.