Hestitaion when accelerating after O2 change
 

So I did my sons type S O2 sensors and the car hesitates when accelerating but still allows to go fast. After 5k rpms it feels fine. We did plugs and wires a few months ago. Cat is 1 year old. Any ideas on what it might be and why would it do this after changing the O2's?

Ps we disconnected battery for 20 minutes. It needs a smog asap