96' Bird Loss of power

hey guys, i have a 96' 3.8 Firebird, and i started it up 1 day after not being used for a week, and i tried to start it, it turned over 3 times, then made a huge THUMP!!! noise, and it felt like my car crashed, and i thought to myself, "that dint sound and feel to good", then i noticed after, battery was dead, jumped it, charged it a bit, and now my car doesnt accelerate like it should be accelerating, idk if this helps, but i just put a CAI in my car, i spent a lot of money trying to fix it, a couple DIY's, i changed the fuel filter, spark plugs, spark plug wires, and the shop put in a new cat, and cleaned the fuel injectors (apparently they were clogged), my pcm is also throwing a code about 1 of my oxygen sensors going bad, could my fuel be running to rich or too lean? my car has a 109,809 miles, and its an auto, :( , but any help would be greatly appriciated, thanks.

Had similar issues with my '90 EFI, but not identical.

While driving at night up a long hill, headlamps and dash started to fade. Pulled over and the engine quite immediately. Dead battery on attempted restart. Was able to leave the vehicle in a parking lot overnight. Jumped the next day, drove to a parts shop that tested and confirmed that the alternator was dieing.

Apparently there was enough of a current being produced to keep the engine running, but using the headlamps caused a net drain on the system, slowly draining the battery.

Hope it helps!