Does this sound like a bad catalytic conv?

[elvis240sx]

sohc 240sx

here are the symptoms:

car runs fine when first startedafter about 20 to 45 minutes depending on temp car starts to run poorly. if i barely give it any gas it will go pretty well, but slowly obviously. if i give it a good hard stomp the engine will rev right up, and hold the rpms for a second, but then start to drop down and have no power. it will kind of shake and do a nose dive. the exhaust physically sounds like someone is holding their hand over it and letting go everyone once in a while. kind of like it is backed up, then will puff out a little, then get backed up and keep doing it. once this occurs, i shut the car off for literally one minute. after turning the car back on, it runs perfect and has lots of power again for around 10 15 minutes, then starts over again. the exhaust does usually have kind of a sulfur or burnt smell to it. the car idles fine when i first turn it on, and also idles fine when the problem begins to occur. i have had the entire fuel system tested and it is perfectly up to specs.

also, car has new plugs, new plug wires, new timing chain, new fuel pump.

if anyone could tell me if this seems that it could reasonably be the problem, or if im crazy that would be great. if im leaving some information out, please tell me.

[dima]

To be shure, check if it is glowing in the dark, Something like cherry color