Help with fuel system

[school boy]

Ok I need a little help before I pull my hair out. Im doing a tpi swap and Im having return line issues. I have the dual tanks with the low pressure efi pumps from factory and an inline high pressure pump. Im was having return line leakage at some of the connector and after using a fuel pressure test gauge found out the fuel isn't returning. It builds pressure up to about 50 psi then rockets to 90 psi. I believe its the tank selector valve. Anybody else have any ideas?