2002 Pontiac Grand Am Very week and drinking gas.

Engine Performance problem
2002 Pontiac Grand Am 4 cyl Two Wheel Drive Manual 70k miles

This all started a few months ago, with it running like my tail pipe was clogged.

Very slow, revving up to 3 or 4 RPM while driving, unable to get above 45, drinking gas, and running VERY rough. Idling very low. It normally idles just under 1RPM when warm. It now idles just under 1/2RPM.

Looked under the car and saw the front and back of the CAT was glowing red. My father had a spare CAT, from a V6 Oldsmobile Silhouette Minivan. I had a local muffler shop install that. (Note: I am aware that this is an over sized CAT for this car, it was free.)

Still running the same way, but a bit better. Had the code read. It showed a multiple miss fire code.

Pulled off the "coil pack" off the top of the engine and test fired the spark pluggs(after buying new plugs). Only the 2nd and 3rd was sparking.

Purchased a new coil pack, same thing.
Purchased a new control module(the thing that screwed into the coil pack), all plugs sparking, pute everything back together and Problem SOVLED!

For a few weeks.

Started running the same way agian with the Check Engine light on agian. Took it up to the local auto shop. The code read "Catalyst System Efficiency Below Threshold". P0420 OBD-II Trouble Code.

Cleared the code, the car started and drove home like it was brand new. For about a week.

Same code agian. Replaced the O2 Sensor after the CAT, cleared the code, drover perfect for about 2 months.

Drove to work on 8/12 Tuesday, ran just fine but a bit sluggish. Went to lunch and the car was running back the SAME EXACT way agian.

Reset the codes, but this time it didn't fix anything, the code showed up agian within one minute and was running the same way.

Now it's in the back yard while I drive another car to work this week.

I read somewhere that I can try cleaning the Mass air flow sensor, unplug the battery for 10+ mins, and that may reset everything. (Sound's a bit too easy.)

Any ideas?
Does this car have an O2 Sensor before the CAT?
MAS Sensor issue?