94 Chevy starting issue

Are there any trouble codes?
What are the components that you have replaced?

Perform the following and see if you can come up with anything.

Fuel System (TBI)

1. Before checking fuel system for a no-start condition, check ignition for adequate spark. Check for proper fuel pump pressure (9-13 psi) and capacity (one pint in 30 seconds).

2. Crank engine, and watch for injector spray. If injector spray occurs, go to step 5). If no spray occurs, disconnect injector harness. Check for battery voltage at harness with ignition on. Battery voltage should be present on one injector terminal. If battery voltage is not present, check for blown injector power fuse. If battery voltage is present on both terminals, check for wires shorted together.

3. If battery voltage is present on only one terminal, connect injector test light to injector harness. Crank engine, and note light. If light flashes, check for stored ECM codes. If light does not flash, momentarily touch test light from battery voltage to ECM RPM reference terminal (circuit No. 430 - Purple/White wire).

4. Each time test light is removed from ECM RPM reference terminal, injector test light should flash. If test light does not flash, check for open in RPM reference wire or injector drive (ground) circuit. If wiring is okay, replace faulty ECM. Before replacing ECM, check ECM power and ground circuits.

5. Disconnect injector harness, and crank engine. If injector spray or leakage occurs, a no-start condition may be caused by excessive fuel being delivered during cranking. Repair faulty injector or injector seal.

When you replaced the pump, did you discard the oval plastic piece that was on the pump between it and the tank unit? That is called a pulse dampener and it will bleed of pressure when it goes bad, which is what it sounds like what you have. Most pumps I have seen come with a piece of fuel injection hose to replace the dampener with