what about plenum? has it been fixed?
take a rubber mallet or a hammer and whack the cat a little, i would bet you hear things moving around in it. Mileage on the truck?
You probably need a new cat
Front O2 sensor needs repalced at least, get a Denso as Bosch sensors dont mesh with these trucks.
However none of this matters if the Plenum hasnt been addressed as it will happen all over again