When the injectors are acting up the fuel pressure gauge is fluctuating between 12-15 at idle
How is this presenting? Is the pressure needle slowly swinging between the high an low? Ir is the needle dropping rapidly, possibly with each injector event?

I'd be thinking fuel pump or power supply to fuel pump.
Fuel pressure regulator or venting problem with gas tank maybe?
Right. First question: Are you using a vacuum referenced pressure regulator? If not the fuel pressure should be very consistent. How the fluctuation presents can help aid in diagnosis. Fast drops may indicate an issue with the volume of fuel being delivered. Slower drops may indicate electrical issues.