Outer Limits 4x4 Board

Can anybody please help me? I have a 90 sierra with stock motor and carb.About 6 days ago i had extractors and a 2 inch exhaust fitted while still using the old catalytic converter(which i think is the original stock cat converter) Today it took its first good run since i bought it (2 months ago) , and it ran like utter shit! It would idle as usual then die and come back as normal, if i tried to accelerate and take off, it would die without riding the crap out of the clutch and pumping the accelerator . Once i got going on the highway, there was an obvious lack of power between all gears no matter what slope i was on. It seemed to be misfiring or not enough fuel getting through, or spark or air, im not sure. I have been using "fuel set" everytime i fill which is meant to keep water out of your tank and keep the carby clean. Any help would be greatly appreciated!!!!!! I am not the most mechanically minded person, but i'm willing to learn........PLEASE HELP!

Hey Ed I had the same problem.......in my case it was a bit of a mixture of things. First was dirt in the carbie i stripped it all down and cleaned it out. This made it run a little smoother and idle better but it still played up. A mechanic said to put some Nulon/Wynns carbie/fuel injection cleaner in the tank because they can absorb any water in the fuel tank which could also be causing the problem.
Since then havent had a problem.

Hey Eff how are ya? Not long after i last posted i have since taken to a mechanic to see what he thought was the problem. He told me what i already thought, which was the carbie was playin up. What he did was switch the 2nd and 3rd spark plug leads over which made the carbie backfire and unblock the jets (i think). Since then i have had to do the same thing a few times, after which she idles fine and has full power. The mechanic told me it was the "fuel set" treatment i was using that stuffed it and it needs a rebuild. When i gear down she seems to gurgle a bit still, and also poppin and gurgling slightly when i rev from a stand still. I assume that the mechanic is right and the carb needs a rebuild. Is a rebuild very hard to do? Does a kit come with good comprehensive instructions? Or should i dump the stock carb and go for a webber or something else?, as i have heard a rebuild only lasts 6-9 months anyway. Also the "fuel set" treatment i was using is meant to do the same thing as a wynns treatment so i am hesitant to try another one.I have also replaced the fuel filter and air filter and also put a secondary fuel filter between the fuel pump and the carb but it still doesnt seem right. your thoughts on this would be much appreciated!!!! Thanks Ed.