i wouldnt worry about a clogged cat,its going to cause engine backfiring popping,hesitation,all the time,sounds like a loose connection to the o2's,check all terminal ends for corrosion,test all terminal ends for the prover millivolts.could be bad o2 sensors remove them they should be a tan reddish color with some carbon,if there al black or white and clogged around the fins def,replace them,id replace them anyways as preventve maintence.