A few general questions

Alright, I have a few general questions, I get a code cat effeciency low.  I just replaced a O2 sensor, and got that code afterwards.  I think I might be in need of a new Cat, but before I buy that, I heard about Catalytic Converter cleaner.  Did anyone use it, and if so, what brand do you recommend?  Also could you give me the GMPart# for B1S2 O2 Sensor, I want to verify that it is the correct part, I don't trust the people at Pepboys.

Also, I am looking to install Fog lights on my truck (97 4wd, 2dr), I was looking at the front air deflector, I want one with openings for tow hooks, and fog lights, does anyone know where I might get one? I checked LMC truck, they only have for older model blazers.

Also I'm having a little problem braking, I tracked the problem to a collapsed hose, it runs to the vacuum reserve, looks like a black sphere or ball on the drivers side, hanging under the hood.  Anyone know what size that is?

Thanks.