I have a 2000 Chevy blazer with the 4.3 in it only cranks.

FIRST > Have a helper turn the key on - while you listen for the fuel pump at the filler neck with gas cap removed .. IF you do not hear the pump run for 2 seconds - check for blown fuel pump fuse in under hood fuse box .... Don't start looking for anything else until you check for the fuel pump to turn on for 2 seconds. Let me know the results.

This is going to be hard to diagnose with any certainty online. Definitely don't want to see you throw more parts at it. Here is a link to to help you find a shop near you.https://repairpal.com/repair-shops Alex

google 2000 Chevrolet Blazer Spider Injector...

Fuel pressure should be around 60psi cranking. Have you check the pressure with a gauge?