Fuel System Issues...

So, I need some input from more experienced mechanics... I recently ran into an issue with my 97 GT not starting, found out there was no fuel pressure to the rail though I could hear the pump running. (I have a Holley in-line system)

I jacked up the car and disconnected the 10an input line to my pump and saw no fuel was coming out. I gave a toot of compressed air into the line and the gas started flowing nice and strong.

I reconnected the line and the car started right up. After 3 days of sitting, the fuel stopped again. This time I've pulled the while tank to check for any debris that could be causing a clog. I've been unable to find any.

Anyone have an idea about what could be causing this?

UPDATE: I swapped the fuel pump out just to rule out that as a cause... The issue remained, I tried pressurizing the fuel tank just out of curiosity and the rail pressurized after that just fine. This caused a large amount of fuel to leak from the tank's return line at the union to the tank pickup, as well. Any ideas why I'd need to pressurize the tank to get pressure to my rail?