94 shaking trouble

Ok, I have a 94 blazer. We've been putting a lot of money into it already so I hope I dont have to put more in.

One of the things in the past I have had done is the erg thing since it had a bit of carbon stuck in it. It would drive fine then shake like crazy and shut off at a stoplight. I had to restart it at least twice. They hooked up the computer to the dash and said they fixed it, then the next day it did it again. They took it out and cleaned it and havent had any trouble.

That was months ago.

Now...

I have two startings.
1. A smooth start that runs mostly fine.
2. A jerk start that seems to start before I fully turn the key.

The Blazer seems to shake a lot. Not as bad when the erg was going bad, but shaking. Some times when hardly any breaks are used. Also when I get to a stop (stop sign or stop light) it is fine for about 25 seconds then it starts to shake a lot.

Also in the last two days I have noticed that sometimes it drives in a lull then suddenly revs up and jerks a tiny bit after I go after stoping at a light or stop sign.

And I have not watched it too much, but I think I might be loosing gas milage.

My brother had this blazer before me and put on a glasspack mufler and I have allways thought any shaking was do to that thing. Could this mean the glasspack is going bad or clogged up?

Recheck the EGR valve and it might be time to do a complete tuneup.