Get UpRev tuned, you'll get better power from your mods, different maps, and that pesky light will be gone for good due to cat sensor readings.

When I get my g3's and motordyne I will.

Any high-flow cat or test pipe that is aftermarket will run the chance of a CEL light. Common fixes are an extended O2 bung sensor or simply resetting the ECU. The O2 sensor is not used to the increased amount of flow or heat that is transferred through causing the code. Usually under normal power loads it doesn't come on but it depends from car to car, hope this helps!

maybe the extensions should come in the kits?

Should but not really their problem. If you look at the Fast Intentions HFC's, they are built with an L joint and extender on it already. You can get em off ebay. the L joints for $30/pair. I bought the straight ones. pack of 4 3" ones for $15 and double stacked on each side. No CEL light since.

do you sell the bungs that help eliminate the ecu code? how much for install? Also what exactly is the function of the bungs? does it fool the existing sensors into thinking that it is stock by pulling it further back from the air flow to slow it down? Just trying to understand it. Any info would be appreciated.

You pretty much answered your own question. Since its running richer, it will throw a cel. Since the sensor is pushed back further, the air/fuel gas will not be read by the sensor.

Hey update...Shout out to Bandit Kaine...if you haven't gotten the hfc's there is a guy selling them for a cheaper price that won't be seen in a while. In my sig is the dyno with the hfc's on there. check it out.