So I had my 99' LT 4.3L home after a rotten seal in the water pump. After the water pump R2, The engine started just fine. drove about 400 yds then a shuddering when I gave it some gas. So I returned back to the driveway.
From there the car would not turn over there was shuddering backfiring and all. Finally it started and idled fine, but give it some gas in P or Dand it starts to shudder stalling at about 2000 RPM. It now will start, but has shuddering w/ any gas.
The only things I messed with while doing the water pump change was the take out the fan and fan clutch, Disconnect the battery, I also flushed the heater core with water to get crap out.
Any thoughts as to what might have happened.

 

Did you make sure to get all of the lines back onto every where they came off. Did you remove the intake tubing? Check the back of the intake hat where the 3/4" tube from the passenger side valve cover meets it.

 

Yes the tubing seems fine. It runs fine for about 1 min then starts missing, I can smell the fuel and see the black crap from the tail pipe. I dont think moisture is an issue as I changed the water pump yesterday.

 

Disconnect the MAF sensor and see if it the problem clears up.

 

I guess I should have saied that I tried that onealready. This thing is just kickin my butt.

 

Yes, please do tell us everything that you have done so as not to waste our time... That would help.

Have you done anything to rule out a plugged catalytic converter?