99 Suburban Catalytic converter and o2 sensor readings - bad cat?

[hometech99]

hi

had replaced cat with aftermarket cat which i heard ups and downs about. i had een told that if you had the capability to see o2 sensor voltage readouts, to watch sensor 1 and 2 (PRE AND POST CAT) for each bank, and tap the gas. the pre sensor shoudl spike up; the post sensor should not spike up so much. bank 2 sensor 2 spiked up before cat replaced.

replaced cat and all 4 o2 sensors (100,000 mi).
after repair, truck runs as new.

after 3,000 miles, truck a little rough. hook up monitor. it reads a pendind DTC, but unknow what it will be.

look at o2 sensor readout again. now, bank 1 sensor 2 spikes up wih sensor 1 (and all o2 sensors are a/c delco new).

did this new cat fail in bank1 (it is a dual cat remember)?