My car was showing codes for a clogged cat converter and was running like it as well.I took the old converters off and they were hollow inside.How could it be clogged and hollow at the same time?

Yes it could be your convertor when the convertor breaks inside it breaks chunk and those chunk bloke the exhaust so no power

If you have a bad o2 sensor or other sensors/solenoid making the car run full rich or full lean it will damage the Catalytic converter and eventually start to break up and clogging up the exhaust...
Try banging on the body of the "catalytic" and feel for movement inside. But if you do decide to replace the converter then make sure you get a diagnostic done on it and fix or replace the bad sensor or sensors that are causing the problem to begin with.
Also know that is illegal to cut the catalytic converter out and run with out it.
Good luck and let us know the results...

code p 0420 refers to cat converter system bank 1-efficiency below threshold ====causes --cat converter---wiring ---Heated oxygen sensor (HO2S) in the manifold before the cat converter
as the cat converter is new , that will not be an option as for the rest if the codes were not prior to the cat replacement , I would suspect wire harness problems from the cat fitment
possible to use a scan tool to reset the ECm

A 2003 vehicle probably did not need a new converter. Cat converters have to be run for years before they clog up. Depending on what kind of vehicle this is, you may have a post catalytic oxygen sensor problem. Also, depending on the vehicle, you can not just replace the converter with any old converter. Many vehicles require an OEM replacement converter in order for the sensors to work properly and these are expensive. Kansas City Converters (available online) sells replacement converters for a fraction of the price that will work with post catalytic sensors and not cause the check engine light to come on.

you have a clogged catalytic converter, it has been recallled for this call the dealer

your engine is fine. find a new mechanic.

if the exhaust clogs it just dies. your cat ( converter) probably clogged due to a very rich condition, which was detected by the computer, hence the light. my bet is a clogged fuel injector or a sensor (either oxygen or air flow) failed. this made it run rich and the cat probably melted.

get a new cat installed, have them run the codes.

You have an overrich fuel condition.
That will make the Cat over heat and in time will ruin it.
Check for codes
Check for misfires
Check O2 Sensors.
Fix the engine driveablitiy issues, and hope converter is okey. Not likely if you caught it so late ,it is red hot.
A ten year old converter being clogged,would seem to me, to have been helped along ,by lack of necessary maintainance on the engine

Sounds like your cat converter has become clogged from diesel....take it to a smog tester to see if cat is bad

it sounds like the catalytic converter is partially clogged my suburban did the same thing and i had i replace mine

clogged cat converter i think.catalytic converter