Rpm won't get over 2000

is the cat. plugged ? check any loose or broken vacuum lines intake leaks , , check EGR , fuel pressure , make sure injectors are firing

I replaced the cat, I replaced the trans fluid. The only thing I haven't done is put a new O2 sensor. I'm honestly lost. I'm 17 and trying to fix my own car cause I need to lean some how lol

so it doesn't rev. up in park ? Does it have the TBI unit like a carb. ? if there's an injector there see if it spits out a good amount of fuel when you rev. it , get a soda bottle poke a hole in the top and use it to squirt gas into the TBI at higher rpm's see if that helps , don't start any fires

It does rev up in park perfectly fine, I think it may be torque converter because some times when I drive it like once in a blue moon the rpm works fine but then slowly stops.