Regulator stuck possibly but it may also be the pump getting hot and starting to fail. I had a similar problem with an external EFI pump. When everything cooled off it worked. Replaced the pump and it kept working. Cavitation and heat will kill the pump. I was fighting cavitation.

I've concluded the external pump and factory style pickup for EFI isn't the best setup. I'll probably sump the tank or get a tank with the fuel pump inside. I don't like coming home on a flatbed.