[Sandwich]

We run the return line to prevent vapor lock. If the fuel is circulating in the system, it has less time to get hot from the intake manifold.
Anyway, the pump could have failed. The Holley pumps we use have a small screen type filter before the impeller. Some times that can get clogged with junk, and prevent proper flow. Also, there is a bypass built into the pumps. There is a spring in the pump that sometimes we have to stretch it out to increase the pressure from the pump