Dumb question. I replaced my converter on my 2003 xtreme blazer.
Is there a converter on the y-pipe also. I'm still having bogging issues at around 1500-2000 rpm and it has no power.

 

Some, if not most, do have a pre-cat on the y-pipe. You can either cut the old one out and weld a new one in or replace the entire y-pipe.

 

Just finished fixing a similar problem on my 97 blazer
The cat died and it's entire contents blew into the muffler wich pretty much sealed it up, however it still ran just felt very sluggish. Fix was a new muffler and new cat
And a bunch of welding to make everything fit and not rattle

 

chances are your pre cat is plugged , I had the same issue on my 2002 turned out to be the pre cat

 

I am having a similar problem with my 02 Xtreme. No power at all. It will idle without any problem. When I drive it, the engine bogs down. Sounds like an old 4bbl under the hood with that moaning sound. Have pulled the post cat 02 sensor out and ran an endoscope in and looked at the cat. The rear section looks pristine. I have gotten OBD codes of P0101, P0301,P0420 since this happened. The cat has a rattle in it too. One guy told me that it could be the cat came apart on the inlet end and clogged up the honeycomb inside. Didn't know if anyone else has encountered this.