Probably a combo of a tuning issue, O2 sensor, or leak. What is the actual code?

 

As stated above, the rear o2 sensors need to be tuned out so you don't get that CEL. I'm sure the cats that Kooks uses are high quality and there won't be much to gain without them. I've had it both ways on the same setup with no perceptible difference.

 

not sure what the code was exactly, but i beleive it was P015D.

 

Well if it was PO150 that is bank 2 sensor 1 circuit malfunction. Might want to check your connections and wiring to your forward O2's. "High quality" or not I doubt they are any different than the cats SLP uses. Toss them!

 

that there's fighting words lol. Don't be hatin for making that money