[Katshot]

There are many things that can cause an engine to stall. Do you have any mechanical knowledge? Have you checked anything yet?
First place I would start is looking for a vacuum leak. A substantial vacuum leak will do what you describe.

 

[Katshot]

Unfortunately, your engine (and ALL Caddy motors since the HT4100) are VERY touchy when it comes to the ignition secondary system. This why back in the mid 80's I started changing my methodology when it comes to tune-ups and ignition systems. On the Caddy engines, I replace plugs AND WIRES at the same time. Yes, I know that mkes the job a lot more expensive but it also makes it a lot more thorough and virtually eliminates situations like this. The biggest problem is the wires. They are SO easy to damage just when removing them to do plugs, that you will damage them without even knowing you did.