I have a 93 Full size Blazer that i've been working on slowly for a couple of years now. I finally got it lifted with 35's, a crate engine and tranny from GM. The problem is (usually)when my truck is cold the engine will stumble and stall out for a second or two and then picks backup and sometimes it will just completely stall out. The exhaust tube that goes into the muffler is no longer welded in place it just moves around in the muffler, but I didnt think that would be cause the truck to stall I just thought my truck would sound a litlle louder until I could get that fixed. Could that be causing a backpressure problem or something? I also noticed yesterday when I checked my airfilter that I have a small leak from my thermostat housing could it be leaking coolant into a cylnder causing it to misfire until the water gets pushed out through the exhaust valve? Any help is greatly appreciated Ive already put so much time and money into this thing and its really gettin to me, I need my blazer to be the Beast it's supposed to be.

 

I would be looking for a vacuum leak somewhere. Also, when the crate motor was swapped in, did you move over your stock intake/throttlebody? If so, then the IAC valve may be sticking. You may want to remove and clean your throttle body and replace the base gasket when you put it back together.