confused yet again

so i had a few issues leading up to this scenario. my fuel pressure was at 35
psi. so i changed the fuel filter first to see if that was slightly clogged. not the
issue the stuttering and wanting to die actually got worse, i then changed the
fuel pump, of course after buying and returning 3 different pumps. i finally got
the right one. drove fine for little bit.then gave me the catalyst efficiency code
bank 1. but its a 4 cylinder. i also just replaced the entire exhaust system from
the manifold bake. but the stuttering and wanting to die and random misfiring
is only getting worse. my next guess is either my fuel pressure regulator maybe
a sticky injector, or a vacuum leak. I'm lost it could also be the idle control
valve. its a 2002 isuzu rodeo 4 cylinder 2.2l the entire wiring harness is from
gm.