Chevrolet Repair: 1990astro 4.3 backfires and dies, chevy astro, oxygen sensors

Question
QUESTION: chevy astro 4.3 carburated engine, the problem slowly came on and now it seems to run smooth and firing on all 6,ive changed plugs wires and distributor/rotor, and egr valve, i also had a exhaust flange leak that i fixed the same time so i think that might rule out clogged catylitic converter. Im at a loss of what i should try next.Ive checked for vacuum leakage and find nothing but i also  dont seem to have much vacuum on some of the lines ive checked. but it loads up when given gas and backfires and sometimes dies, it will go  and i can get up to speed but its really hard and it takes off so slow i can barely keep up with traffic.  any advice would be really appreciated

ANSWER: HI JAMES,THIS IS NOT A CARBURETOR ENGINE IT IS THROTTLE BODY,FUEL INJ..THEY WAY YOU ARE DESCRIBING THIS IT SOUNDS TO ME LIKE IT MAY HAVE A PARTIALLY PLUGGED CONVERTOR...THE BEST WAY TO CK IS REMOVE BOTH THE OXYGEN SENSORS BEFORE THE CONVERTOR. DRIVE IT LIKE THIS AND SEE IF THE PROBLEM IS BETTER,IF SO THE CAT IS PLUGGING UP..THIS WILL BE LOAD LIKE THIS BUT IT IS JUST FOR A TEST ONLY...THE FACT THAT THE ENG RUNS SMOOTHE TELLS ME THAT MECANICS ARE OK AND IGNITION SYSTEM IS OK..BUT THIS MAY HAVE A JUMPED TIMING CHAIN..BUT USUALLY THEY DO NOT RUN GOOD LIKE THIS.. ..LET ME NOW HOW THIS WORKS OUT FOR YOU,AND GET BACK TO ME....GOOD LUCK,, TOM..

---------- FOLLOW-UP ----------

QUESTION: ok i tried unpluging the sensors   no difference and i tried several sensors to see if it would have an affect, and it still backfires upon givin gas.....what i have discovered is that when the motor is cold it runs great and doesnt backfire, but when its hot and it gets hot very quick, it reaches the max.hot before its too hot  a little too fast. when it is hot and i attempt to drive it spudders and spuders til it gets up to speed  and is very slow, wont go uphills

Answer
HI JAMES,I DO NOT WANT YOU TO DISCONNECT THE O2 SENSORS ,,,I WANT YOU TO REMOVE THE O2 SENSORS FROM THE MANIFOLD BEFORE THE CONVERTOR. DRIVE IT LIKE THIS AND SEE IF IT IMPROVES. IF SO THE CAT IS PLUGGING UP...WHEN CATS GET HOT THEY RESTIRCT MORE..LET ME KNOW,,,TOM