Hdchevyclassic

Need some opinions on what the heck is going on with my 2007 silverado classic. It has a 4.8 litre vortec with an afe cold air intake, edge cts2 programmer, gibson shorty headers, and a 3 inch catback exhuast. I have the code p0430 coming up but cant figure out what it is. Ive done a back pressure test on the cats, and did knock sensors and all O2 sensors a year ago. It doesnt feel like it has a misfire and im very mechanically inclined and everything in this truck is looked after. When i bought it there was a 4wd code and it wouldnt engage so i swapped out the button cluster in the cab and now it works fine. Other than that the truck has been perfect but id like to figure out what the heck is setting off the code. I have no exhuast leaks and the cats checked out perfect, anyone know what else it could be? Im looking for anything at this point, i hate check engine lights and have cleared it with the programmer but it comes back very shortly after being cleared. Thanks