The wiring diagram for the 3.4 shows only 2, one downstream of where both banks join, the other after the cat. My 01 3.4 Alero had only 2, and my 00 3.8 Impala (also OBDII) has only 2 as well, in similar locations. I guess they can save $$ by not using more.

 

Hmm...Ok.

 

Ok so I changed the cat, officially, and the car runs like new, thank god!
I did not change the 02 sensors.

Thanks 4 all ur replys.