I had a 94 with 5.7 TBI that was doing the same thing. I replaced plugs, wires, rotor, cap, and icm. None of it helped. Then I happened to read, on some obscure and now forgotten corner of the web, that an overheating icm can cause this exact issue (runs fine when you first start it up, but bucks and dies when you give it throttle at normal operating temps). So I went to BestBuy and bought a tube of thermal paste, which is used to dissipate heat between components of high end computers. I removed my icm, coated the back side of it with the thermal paste, and reinstalled. I never had another issue again.
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