my exhaust is killing me, manifold gaskits are just starting to sag out the bottom of manifolds, but when the truck is cold it runs fine, warms up and it sounds like open headers sometimes, and it will calm down. then if i stop at lights or a stop sign when its quite, when i go its wide open. could it be my cats are shot, or ?.

 

TRy replacing your manifold gaskets. There is no reason your cats should be failing if you have taken care of your truck.