Sluggish acceleration and rough shift change

My 2003 honda pilot check engine light as been going on and off for the past couple of months ever since I changed the catalytic converter. Mechanic replaced the oxygen sensor
and said that if it comes back on, it might be a defective catalytic converter. For a few days now the check engine light blinks at times and the vtm-4 light comes on a few minutes later. The car has noticeably power but it doesn't sound like any of the cylinders are misfiring.
your help much appreciated. Thank you.