1999 Chevy Silverado Still having problems

Engine Performance problem
1999 Chevy Silverado 6 cyl Four Wheel Drive Automatic

I have a 99 Chevy Silverado 1500 4.3L 6 cyl. Had to replace the transmission, but it sit for awhile before I could get fixed (of course), but when the work was done. The mechanic decides to tell me that it was running a little rough and I needed to run some good fuel and fuel treatment in the tank and it should fix the problem or maybe replace the fuel injectors. They did perform a tune-up on the truck while they had it, but the check engine light is still on and it was running really bad. My general mechanic gave it a look over and replaced the fuel filter, O2 sensor, and the battery. He replaced the distributor cap with another used cap! Kept coming up misfire codes on 1 and 5. Took it to a muffler shop per advice of friends and they told me the catalytic converters were bad in the truck. Replaced those. And now the truck will not even turn over. It tries, but sounds like it just cant do it. I replace the ignition coil thinking maybe it was that, and here I am, it still didnt work! Where do I go from here or dare I ask? Really hit me in the pocket as of late.