Funny you should mention "stealership."

Those are not symptoms of catalytic converter problems. Cat symptoms fall
into two categories: those that announce themselves by the "check engine"
light coming on and those caused by the catalyst becoming plugged. You don't
have the first, with codes that point to the cat, right? And plugged cats
are more of a problem when you push on the accelerator than they are at
idle. Sometimes they have chunks of sintered debris floating around that
cause intermittent stumbling, but again that is more of an "on the road"
problem than an idle problem.

If the tune-up parts (spark wires, rotor, cap) haven't been changed since
new, now is the time to do that. Use only OEM - new aftermarket forms of
those parts have been known to cause grief. Change the spark plugs, too, but
you can use NGKs for those if you want. Cover another base by adding a
bottle of Techron to the tank, unless you have been using "top tier"
gasoline semi-regularly. If the problems still persist we're looking at
intake problems... or possibly ignition.

Mike