I'm feeling pretty sure about what going on with my old S10, but figured I'd throw this issue out there for review just in case.

Starting 2 weeks ago my blazer started losing power on acceleration, especially under a load (acceleration or going up a hill) it has gotten worse daily at a fast pace.

My initial urge was to think it was an Air Flow Meter(mass air flow)problem. Yeah I know this vehicle doesn't have a MAF, but that's what I mentally associate those symptoms with because I'm a certified Nissan Tech and I'm so used to MAF's causing this exact problem EVERY DAY at work. Gotta remind myself I'm back on a Chevy product not a Nissan. Anyway, since I know these don't have an MAF I assumed it may be an IAC valve issue or something related to air intake control (similar to MAF...) and have been expecting to need to replace that soon...... I think I was wrong to assume that.

Yesterday the problem got ALOT worse. Misfiring big time, no acceleration, but I had no time to work on it.

Today... much worse again. Misfires were worse and had even less power. Can't even get up to the speed limit (had to try to drive to college today because I was late.. shouldn't have). When I tried to accelerate it bogged down even worse and the vehicle would hardly even crawl back to my house with a line of traffic behind me. It started eminating an extremely HOT metallic burning smell. At one point is sputtered even worse and the check engine light came on for a minute then went back off (probably just misfire codes, havent checked since its back off).

Later Today... I was sitting here thinking about how I shouldnt have tried to drive it today. I'm actually a good mechanic and troubleshooter on most vehicle types and would have shamed anyone else for doing the same but I have this hatred for fixing my own cars muahahaha can't help it. Anyway, I was sitting here and realized that my subconscious had been hearing rattling noises under the truck that sprang up suddenly a copule days ago and I could just smack myself now for not realizing it was a Cat Converter that was causing all of this.

So... I think I've got it figured out, but havent even bothered to crawl under the truck to check yet because I'm feeling particularly lazy today and wanted to ask here first. (shame on me) Anyway care to lend their Chevy experience to me about these symptoms just in case there is something else that may cause this too?

Recent Work I've done to it. Tune up (wires plugs air filter) Replaced fuel pump (in tank.. that sucked) and the pump filter, o-rings etc. All within last 5 weeks.

Everyone here has permission to call me names for missing the obvious explanation for this problem

 

All your symptoms do sound like a busted up cat. My blazer had all the exact same symptoms as yours except for the mis-fire, after I removed the cat I found the honeycomb was in pieces, sometimes it would almost run fine and others there was no power at all above 1300ish RPM. I believe that the busted pieces were acting like check valves and the exhaust pressure would force a piece into the discharge side and plug it off. As suggested in here before, try removing the O2 sensor and see if it runs any better, this will give the exhaust a place to vent...it won't run perfect but will let you know if you have a restriction or not.