I recently did lots of exhaust work on my '01 SE. I have 2 new catco universal cats downstream. And two new catco cats that are up by the headers. And a new Flowmaster muffler equipped w new tail pipes. All recently replaced due to upcoming registration and CA smog check. Little did I know when I took it in they neglected to probe the exhaust and even run the truck on the dyno. So I asked the technician why no probe and detailed readout with emissions levels and whatever. He told me 2000 and newer only require ECU check with OBD II reader and visual inspection. Nice!!! Time to get creative with new exhaust next time.