I have a 97 z28 and the car is hard starting bad. Once it finally starts the car idles real hard because of low fuel pressure and then after about 1 min the pressure jumps back up to about 41-43 psi. I have changed out the fuel pump about 4 months ago along with a fuel pressure regulator and fuel filter. What could this be?

 

Are you having a problem with the charging system? Does the dash volt gauge run in the red when the fuel pressure is low? How low does the pressure drop at idle on startup? When the pressure "jumps back up to 41-43psi", if that's with the vacuum line connected to the fuel pressure regulator, its a bit higher than I would expect. Typically you will see 36-38psi at idle with the vacuum line connected.

Have you checked the fuel pump relay?