Bad hesitation under acceleration

[3R1CD4V15]

1997 gtp
stock
156k miles

This problem has gotten way worse now. I used to just have a pop sound under load, but now it is bad hesitation if i go above 2500 rpms.
The rpms will drop down about 200 then come back up until i let off the gas.
I have sel codes p0420 and p0300.
I replaced cat and fuel filter, disconected the battery(does that reset codes?). And still have the same codes...

I would say it has gotten worse since i have done these things.
The old cat didnt look bad. replaced with a zzp high flow
the old fuel filter was bad tho, I could barely blow thru it...

I took one plug out to look at it and it looked brand new. (a little black on the white part)
The wires look brand new also.
Ive had this car a little over a year and the plugs and wires look like they are maybe 2 years old?

I think I am gonna pull all the plugs to look at them to see if this could be a simple fix.
Then maybe rent a fuel pressure tester.

Any help would be much appretiated.

Thanks,,
Eric

 

[Fivefingerdeathpunch]

Replace all spark plugs.

 

[3R1CD4V15]

Replaced Plugs and wires.

All codes are now gone.

Car is fixed.

 

[Mike Kopstain]

Yeah most problems like this are going to be ignition related. The wires can look perfect too and still be completely F'd. It's cheap insurance to replace that stuff.