need help with 93 4.3L v6 silverado

every time we crank it, it idles rouph and when we give it some gas it spits and sputters, backfires out of the throttle body, and seems to be flooding. It wasnt running due to no gas getting to the throttle body because of the wiring harness but we fixed it. The problem with the wiring harness was that it backfired out of the throttle body w/out the breather on and caught fire. We replaced the air filter, engine tempeture sensor, spark plugs and wires since. PLEASE HELP!!!

Check firing order. Does it have a lot of miles? It could have jumped time or could have a bad valve. I would first make sure all the plug wires are in the correct order.