OK, In just saw this thread and notice the guys here have been doing a good job trying to work you through your issues. As you have already noticed, when you have multiple issues at once, it is more difficult to diagnose and eliminate them one by one.
A few things I noticed after reading the whole thing:
1) You should still look into replacing the old O2 sensor, as I don't see that you've done that yet. In answer to your earlier question, you should have two O2 sensors, but you would do fine just replacing the sensor on bank 1 (in your rear exhaust manifold).
2) You should still check out your CAT. Get under the car when it'* cold and bang on the cat. If it rattles, then you should definitely replace it. Or take it to a shop and have them check the back pressure (a more definitive way to know).
Oh yeah, I just realized that you said you bought a code reader. Is it just a code reader or a scanner that will give you live data? Reason being, a scanner can easily indicate whether your O2 sensor(*) is/are bad. It will also gve you an indication of your Cat'* performance.
3) I didn't see anywhere that you have checked/replaced your fuel filter. It'* an inexpensive maintenance item that should be done anyway every 50,000 or so miles.
4) With the misfires you are experiencing, yes, you should check/change those plugs and wires. Use AC Delco or NGK TR55 plugs and AC Delco or Belden wires. Frankly from your last post, the wires sound like a likely culprit.
5) Double check all battery cable connections, both at the battery and at the terminal ends. Check for corrosion or looseness, even under the cable end boots.
Let us know about each of these items and we can go from there.
As far as the shaking problem, I suggest you start a seperate thread for that, for better focus. But maybe wait until you have the engine issues resolved first to keep your
Mike: 1997 SE w/ 183K, aka White Horse
, Gutted Airbox w/K&N, drilled 180* t-stat, tint all around, clear corners w/SilverStars, "PONTIAC" light up tail, PEMs, NGK TR55s