I have an 03 Cobra with smaller blower pulley, diablo tune and added Bassani X-pipe while back.

I've been throwing a P0153 trouble code Slow Response from O2 Sensor. I'll clear it and drive it for some time and it'll eventually come back.

Is more likely because of the mods I've added, or an actual problem with 02 sensor, exahaust leak, or Mass Air sensor?
I just do't want to go off chasing the problem in the wrong direction.

Any help is greatly appreciated.

Thank you.