4.3 vortec V6 running terrible

[leegreen]

re-read post 12 above
Your exhaust could be plugged.
You have spark. Pull a plug and see if it smells like gas to confirm you are getting fuel to the cylinders. Might even be able to smell it in the oil if you cranked it enough

you said the cat was rattling but you shook the chunks out and it is now gutted. Can you see right through the pipe now? Cat can break up but still be blocking the pipe. Getting a crowbar in there and smashing all the ceramic is the only sure way. Unless you can see right inside you probably need to cut it open.

Drop the y pipe and see if it starts.
I had a 4.2 inline 6 that put up a cat efficiency code one day and stopped dead on the side of the road the next. I pulled the upstream O2 and it started and I drove it home breathing through a 3/4 inch hole. It was down on power a bit though.

[straight6chevyguy]

Ok thanks for the comments.
But I guess I need to make this more clear:
I have taken the complete y pipe with cat attached off and out from under the truck.
Going off memory I believe I ran a rod or bar of some kind into the cat and broke up the remainder of the inside contents and shook out all of it out on the ground till nothing more came out then I looked into the pipe through the cat and did not see any restrictions or anything blocking or anything left in the cat that I could tell. I could see through the cat to the opposite end of it where the y pipe attaches to it. Currently the only exhaust pipe that is attached to the engine in the truck is the y pipe and gutted cat. The muffler and tail pipe are disconnected.
I am 100% sure that that there is no exhaust restrictions.

[straight6chevyguy]

I'm honestly leaning towards my problem being either a fuel injection issue or a timing problem could it be a problem with the ECM?
I'm going to try starting it again today and I'll try pulling some plugs to look for fuel.

[3drburb]

Now is a good time to put the scanner on it, before trying to start it again.