[THEFERMANATOR]

This is a 350 or 5.7L engine with a distributor correct? I have never seen one, but I have heard some 99's came with the 4.8 and 5.3L engine. I just want to make sure. As for your O2 sensor, there is one after each manifold, and one after each cat. If you straight pipe it it will go into engine protection mode and limit the timing WAY back. I do NOT reccomend doing it as CAT's aren't that expensive if you get aftermarket MAGNAFLOW universal ones(last ones I bought were $65 each). With the P0440 code, there is a GOOD chance your WHOLE problem is nothing more than a stuck open evaportive emissions valve venting fuel vapors to the engine and fattening out the mixture. This will cause it to be off on the timing tables and show both cats as having poor efficiency.