P0175 too rich

Well, just got a P0175 code (system too rich bank 2). I'm leaning towards the MAP (manifold absolute pressure) sensor or the oxygen sensors.

Any other ideas?

Do I have to replace all O2sensors at once? What does "bank 2" mean? Does it means "before the cat?"

Can I clean the MAP or does it need replaced? What is the difference btwn MAP and MAF?

97 Jimmy 4.3 W 4WD
new plugs and wires, cap, rotor, pcv, fuel pump, ignition switch, fuel and air filter, cleaned EGR and TB, new floor mats too !!

Also, about two weeks ago, I had a P0420 (Cayalyst Efficiency below threshold - Bank 1). I changed the plugs, cap, rotor, and wires - cleared codes by battery disconnect for 15 min -- and the codes went away. Now I've got the new P0175 ...

ideas or advice?? Thanks!