1997 Chevrolet Blazer • 170,000 miles

The suv ran great for a week, then back to its old tricks, impossible to start. I have replaced the crank sensor (coil pickup), rotor, fuel pressure sensor, fuel filter, fuel pump, battery, spark plugs, and plug wires. It has spark, and holds between 55-60 psi fuel pressure. I simply cannot figure out why this vehicle starts/refuses to start so sporadically. Any 4.3 vortec specialists out there that can give me a clue in the right direction?
July 24, 2013.

Scan for codes and check fuel pressure first. Fp should be 60-66 psi so it may be a regulator it should also hold that pressure for 5 minutes after turning key off

Jul 25, 2013.
If the fuel pressure regulator is a small screen and diaphragm under the throttle body, I have replaced that as well. The list has gotten so long that I forgot to list it above.
The part that absolutely puzzles me is that it refused to start, then ran fine for a week, then refused to start again. Could all of this be attributed to a timing issue?

Jul 26, 2013.
Do what I suggested first

Jul 27, 2013.