It's the original stocker. Car cranks but won't turn over. Put a pressure guage on it and when you turn the ignition to the on position the pump primes and the guage shoots up to like 50psi then gradually falls down to like 5-10psi. The filter was replaced with the last 7k. Is this the pump or possibly still something else?

 

You have a slow leak somewhere. Check the cross over from rail to rail. Mine was leaking and had a steady drain on my fuel pressure. When I had no leak I saw my pressure climb when I turned the key (engine not running).