1998 Jimmy Starts but then stals imediately after

My 1998 Jimmy SLE 4.3L is having issues starting. The vehicle will start but then stop when it settles down to the idle rpm. When i turn the key I get a fuel pressure of around 52-54psi and i can hear the fuel pump running. The odd time when I can get the vehicle to run I get a fuel pressure of 55psi and the engine runs better than it ever has. Since the problem started I have changed the following:
Cap and Rotor
Spark Plugs and Wires
PCV valve
Fuel Filter
No codes showed during a scan and the problem occurs often but occasionally it will start without a problem. My last thought it would be a fuel pump or a fuel pressure regulator. Again, I can hear the fuel pump activate when i turn the key and the fuel pressure is just below 55psi when i turn the key. Any help on the problem would be greatly appreciated

Vortec needs at least 60 more like 65 psi.

Also symptoms of a cold hard start, could be a dirty or bad MAF sensor.

I agree with maxwedge on the pressure. Low fuel pressure is the problem, guaranteed. Key ON, engine OFF, fuel pump running, pressure must be 60psi to 66psi and must remain above 55psi for at least 10 minutes after the pump shuts off. Best to check it at the fuel filter by modifying the tester so fuel flow ends at the tester. Pressure must be 73psi to 108psi and must remain above 55psi after 10 minutes. If not, check power and ground at the module, if ok, replace the fuel pump. If it runs better than it ever has with 55psi, wait til you get 60+ psi ;)