I have been getting poor gas mileage lately and I checked the fuel pressure and noticed that it would drop rather quickly after the fuel pump was turned off. It would go fro 45 to 20 psi in about 5 seconds. I thought that maybe I have a leaking injector so I pulled the fuel rail. I then pressurized the fuel rail and checked the injectors and they all seemd fine. No leaks or drips. What else would cause this? And is it really a problem? Could it be the adjustable FP regulator?

It could be the AFPR, the Holley AFPR is designed to release the fuel pressure after priming if the car is not started. The other possibility is a bad check valve on the fuel pump in the tank and I know you don't want that. You can check the AFPR by pinching off the fuel pump return line and priming the system. If the pressure holds, that is the culprit. If it doesn't hold, then I would suspect the fuel pump check valve.

I'm thinking if the AFPR has a slight internal leak it really shouldn't be an issue, as long as it can maintain pressure under full throttle. I just know that the system use to maintain the fuel pressure after the pump was off and that is why I thought the injectors were leaking.

It wouldn't be an issue unless the diaphram inside it was ruptured.

Its not really a huge problem. You wont damage anything if you dont fix it. About the only thing you might notice is longer crank times.