would drive it for a few miles get it al nice and hot and repeat this over cold to hot starts then see what you have anything after thus is a fault somewhere,, bare in mind cat dont start working until gets to around 600c as do the 02 sensors , i would live data it look at coolant temps, look at smooth running and injector corrections and 02 sensor voltages on signal ie a engine run for a good hour at 3000 revs should have a 0.7volts middle value fast changing on pre cat and slower changing on post cat sensor,