new engine wont run

I have a 91 s10 with a rebuilt motor I just put it aint I cant get it running. My old motor ran perfect but smoked like crazy so I was guessing rings were worn. I got the motor and put my old intake/ tbi back on and when I went to crank it up it would run shortly ok and then when the choke would let off it would die immediatley unless I flooded it to keep it running. I took it to a shop and they told me I had an intake manifold gasket leak, and I'd also have a high idle due to a bent throttle body shaft?-and to replace the throttle body. I towed it back home and swapped out the gasket and used a little silicone to seal it better the 2nd time and tried it again and it ran worse and wouldnt hardley run for a second or two. I thought maybe the intake was warped or cracked so I found a used one on ebay for 20 bucks and tried that, along with a rebuilt throttle body. That didnt work either. It will just turn over and pop and run for a second then die. I left the timing where the shop had it set to the first time and also played with it a little and it made no difference. I talked to a neighbor of mine and he said his dad had one and it had low fuel pressure and was a bad fuel pump. I swapped that out and the filter, and nothing. I talked to another mechanic and he said he ran into a problem similar on a 4.3 where the new motor installed had a cam that was for a carburated truck instead of a throttle body. I dont know what else to try.

Did you set the timing with the black and brown timing wire unattached from the PCM under the glove box?

Sounds like the timing is off a bit seeing when it goes into closed loop it won't run.