I agree with Dozzer, you may have to add an aftermarket fuel pressure regulator. You need a computer you can hook up to the engine while its running and see what's going on with O2 sensor and fuel pressure and timing. You may need to find a hot rod shop that tunes computer controlled engines and let them tune it. Have you gotton with Holley Tech? You may need to go over your specs with them and see if they can locate the problem.

I have built a couple 383 TBI engines with stock TBI and did nothing but put a performance chip, and boost fuel pressure. I have never even had to get a custom chip. Most have been about the same engine, so I say get with Holley on their TBI.