2002 Chevy Prizm Hesitation after 2 new O2 sensors.

The car was giving me a code, I forgot which one, but indicated that either the catalytic converter or oxygen sensors needed to be replaced. I bought 2 new bosch brand oxygen sensors, one oem fit, and one universal fit. After replacing the sensors I reset the computer and took it for a test drive to find out that it was hesitating majorly almost to the point of stalling about once or twice everytime it isn't fully warmed up. Re-checked the sensors to make sure they were installed tightly, rechecked the wiring on the universal fit to make sure it was wired correctly (it was), and now I am stuck. This is the only thing that was changed and the car is in worse shape now than it was before I started. I read on this site about checking the Mass air flow sensor and I visually chekced it, looks clean and fine. So my question is, can the catalytic converter be so clogged up that it is giving a huge difference in readings between the O2 sensors and causing it to stall? Could it be the bosch sensors and not oem ones? Or any other suggestions? Thank you for who ever answers this.