P0420 & P2096 help
 

Recently did a midpipe swap from the previous owners midpipe (unsure of brand possibly Agency or Ebay special) to brand new Turbo Xs Hi-Flow Cat with matching cat-back. Put in a new O2 sensor with it since I was already under there.
I got the expected DTCs after the swap. I downloaded versatune and flashed it with their prebuilt for my exhaust system and did the 20 mile drive they recommended.
Driving in to work today i popped a P0420 and P2096 code for being too lean on downstream and Cat inefficiency. I plan on starting at the airbox to trouble shoot and see if there is any cracks along the way. Any other places I should be looking to troubleshoot for these codes? I haven't put the K&N panel filter in yet since the codes popped up.