Been noticing very sluggish performance then the light came on.

Ordering new Y with 2 cats

 

I maybe wrong, someone correct me if I am incorrect.

So you performance is sluggish - and your light came on?

The only way the cats can effect your performance is if they are becoming plugged. I had and issue once were the stainless wrap that surrounds the core (looked like steel wool) was gutting sucked up into the header and it allowed the brick /honeycomb to turn sideways in the converter housing. Now this issue was noticeable and the engine wouldn't rev like it should. This still did not set a code on an OBD II 4-valve Cobra. Also once ran leaded VP race fuel thru my one 5.0 and melted down a cat - once again no code, just sluggish throttle response noticeable in park working the throttle - Do you have this symptom?

So what code did you get that says your cats are bad? Once again correct me if I am wrong, but if you are cats are failing I am not sure theirs "bad cat" code and if yours are getting plugged you WILL notice in park revving the engine is sluggish..

 

P0430 and P0304

This all happening couple days after I heard knocking from bottom of engine. Then the one day the knocking went away. After 30 mins of driving these code came up.

Days leading up to this the acceleration was poor after 10-15 mins of driving almost to the point I couldn't even pass.

Im not sure If i did damage to a cylinder but once new cat arrives I will be able to tell.

For now I do not drive my Hummer till I get this fixed

 

So you have miss fire code (driver side #4) and cat efficiency code driver side.
1. Did you check for spark on #4? Could have failed coil pack
2. Did you do tune up lately
3. Did you try clearing the code first?

As I said earlier our trucks have 2 cats bank 1 & bank 2
If you do have a bad cat you should replace both.

 

Changed plugs
Ordered Y pipe which has 2 cats

I say changed cat cause it's one piece not exactly efficient to change just one.
My plan now is to keep current Y once new one arrives and in spare time maybe cut cats off and go just pipe or high flow cats either way it gives me options

 

This seems more concerning than the cats. Have you drained the oil? Is there metal in the oil? IS there oil? Knocking in the bottom end is typically not a good sign