Idles well till warm,then step on the peddle an it shudders an dies
 

Ok so I just bought this 2000 ss Monte Carlo,owner said if transmission warms up it stalls.so ok,I think its a awesome car,I bought it.but after driving it 2 miles to my house no issues,so I tested it,stepped on the peddle to get it to stutter an stall,an yup after a few times it did,let it sit for an hour or so,tried again,only now I went start,an if it does it lasts a few seconds to a half a minute.im thinking its a combo problem,1 fuel pump fail,2 air flow vent,3cpu corruption, any ideas? Ill do a full tune up an post my results.

I would think this is the fuel pressure regulator or fuel sending unit failing.

Given the age and typical miles of these cars, they could just need some neglected scheduled maintenance.
- Inspect the oil. After running the engine, shut it off and with the engine off, remove the oil cap. Take your finger and get a swab from inside the valve cover. Usually if the lower intake gasket is failing, this is a good spot to inspect (sometimes shows on the oil cap and when really bad shows on the dip stick). If the oil looks milky, you are probably i need of changing the lower intake gaskets.
- If you have no idea how old the spark plugs and wires are, I would change those. Get some good plug wires (AC Delco or BOSCH wires are what I typically use) and get some good plugs AC Delco or NGK platinum plugs are my favorites, NO BOSCH PLUGS). Change those.

Those are the first starting points. This thread can also give you a ton of other maintenance items to address:
https://montecarloforum.com/forum/fw...0-miles-46078/

Curious about the specific wording of the transmission warming up, not the engine. Does that imply that it only occurs in gear or does it happen in park also?

As for cat vs fuel - that should be easy to determine from a quick scan of the sensors. If fuel trims are pegged already and it stalls when you give it more gas, that would be fuel related. A bad cat would give more normal fuel readings, but generally hits a wall at a certain rpm where it can't flow any more exhaust despite seeming to run fairly ok elsewhere.