My friend and I are trying to figure out an issue with his car. It is a 1989 Camaro with a ls1 swap in it. It has a Aeromotive FPR and a walbro 255 pump. A few times it has been sputtering and running bad and the fuel pressure would be down to like 7psi. Then we would turn the car off and 20 minutes later it will start right up with good fuel pressure. It happens when there is about 1/4 tank or below of fuel. I was thinking it's just from low fuel and he should keep more fuel in the tank. But there is another issue that still doesn't make since..

The fuel pressure bleeds off (engine off) rather quickly. I'm not sure what the spec is for these cars. It dropped from 55psi to 45 psi within 1 minute. It will continue to bleed all they way down to 5psi within about 10 minutes.
We pulled the return line off to see if it was leaking from there, it wasn't. Then we pulled the fuel rail off with the injectors attached to see if any were leaking, none were leaking. So the only thing left would be leaking at the pump. Well we dropped the tank and looked at the pump. Everything looked good, no cracks in hoses or loose wires. Any suggestions?