I'm getting 12, 13 and 44. Does this indicate that I should replace the O2 sensor?

 

12 is nothing,its telling you that your in diagnostic mode.

Replace the 02 sensor,and it should be fine.

 

I did and the CEL is gone.

Now I have to deal with the lack of power.

I'm almost positive that the original cat is on the Blazer. The old O2 sensor was just about powder coated black so I'm thinking it is time to replace. There is hardly anything coming out of the exhaust pipe. If that doesn't do it I'll replace the muffler.

The symptom I'm seeing is that when first started it seems alright. Not full power but enough to get me where I'm going without too much trouble. After a few miles it dogs a bit more. It takes a while to get up to speed. No backfires, just anemic.

If I still have an issue I'll look at replacing the spider.

 

I replaced the cat and it seems to have helped, at least with the exhaust. I can feel a marked improvement in what is coming out of the tailpipe. I will have to replace the muffler as I saw where it has separated on the back seam.

My drive home indicates there is some more power but I won't know for sure until I drive her to work. If I don't see the same response then there is an improvement. I just don't think it solved my problem. After replacing the O2 sensor I haven't had the CEL light pop up.

I think I need to look at the spider next but I would like confirmation.
Should I disconnect the battery to reset the ECM?

 

I have read you can just remove the ECM fuse for 30 minutes to reset any codes. I have heard both that way and the battery way work, just doing the ECM you wont have to reset your radio stuff ect.