1991 Chevrolet Silverado k1500 Idle/fuel issue

Ok here is the problum I have a 1991 Chevy k1500 350 5.7 that is having idle issues and seems to be loading up. It has problums starting and when it does start it is either starved of fule or loads up. When I bought the truck the return fuel line was crimped off so I replaced the fuel lines. At the same time I rebuilt the throttle body and cleaned the throttle body. At this time I also checked fuel pump at this time and it is good. After doing this I tried to start it and it still did the same thing. So I then replaced the temp sending unit, throttle positioning sensor, map sensor and idle air control. Start it up and still dose the same thing. So I checked timing and it was off a little so I now have it at 5 degrees advanced and it seems to idle a little better. But then I go to take it for a spin and when I go to take off in 1st it seems to load up or is starving for fuel still. Only thing I have not replaced is the o2 sensors. I have replaced cap router and plugs and wire. Any ideas would be greately appreciated.
If I cant get it to run dose anyone know how hard it is to convert tbi to carb?