Losing fuel pressure

[agtech]

I just finished building a fuel system for my 1992 LX. I built a rear sump on the tank with dual outlets, -6 lines to inline Walbro 255lph pumps mounted behind the tank, -6 dual lines to the engine, one to each rail, TMD 1000hp billet rails, dual lines running to Aeromotive EFI regulator fastened in front RH shock tower, single return line to tank. Engine is a 9.8cr 306, Twisted Wedge heads, Performer RPM intake, 24lb inj, C&L 76. Dyno'd at 300rwhp.

Anyway, the car runs fine until the engine warms up to operating temp. Then fuel pressure starts creeping down from 38 psi where I set it. The pumps start to get noisy as pressure drops. Soon driving pressure is 20 psi, and if I step on it at all, it drops to 15 or less and then lean bogs and backfires. The first time it happened I opened the lines to check my fuel filters and there was all kinds of vapor pressure in the line, even after the car was off for 10 minutes. I reconnected the lines and turned the key. The pumps were quiet and pressure was good. I drove it another 2-3 miles and same thing happened. Then I opened the line at the regulator and same thing, lots of vapor pressure.

It seems like the fuel is vapor-locking or boiling in the rails. My engine runs a little warm, maybe 190 to 200, half way up on the factory gauge. The fuel tank is full. I'm going to try and get the engine to run cooler maybe try driving without the hood to diagnose if it's heat-related. The car ran 100% before the fuel system upgrade. I only did it because the stock lines can't support my 150 shot wet kit. Any ideas?