Chevrolet: 2001 impala dieing at low speeds, catylitic converter, o2 sensors

Question
I have a 2001 impala that occasionally dies at low speeds or when idleing for a long time.  I took it to the dealer and they hooked a diagnostic machine up to it and found nothing.  Someone else with an impala said they thought it might be the catylitic converter.

about a year ago I had the transmission lines in the radiator break and had to have the radiator rebuilt.  That is the only major work I have done to it, but i have only owned the car for 2-3 years.  

Answer
If your manifolds are not glowing red then its not your cat.

When was the last time you changed the O2 sensors, fuel filter, and spark plugs?

Change those first and also clean out the ThrottleBody and intake idle air control module mounted on the TB.