O2 Sensor "too Much Activity"

I have a 2003 Impala with 3800 series II. I have replaced the single exhaust with Dual cat backs (gm performance parts exhaust) and a 3" Hogan front downpipe with hi-flow cat. I also run a K&N intake. When I installed the downpipe, the engine light came on and the problem it says is too much activity on the #2 oxygen sensor (located next to cat). The fellow I bought this pipe from said he had the same problem with this pipe on his Grand Prix. Is there a fix for this? I have currently installed an O2 simulator (basically a sleeve that draws the sensor out of the pipe a bit) and I still have the same code. What is my best bet?

Thanks in advance

There is an O2 sim available that allows you to remove the O2 sensor entirely, and it simulates the signal for the PCM. I'll try to find a website for you.

Never mind, Hemi beat me to it, thanks!

For reference, this is basically normal upstream activity on a 231 V-6:

http://www.wwdsltd.com/files/231V6O-SensorActivity.jpg