67 twin turbo dart

Matt what fuel are you running and what size injectors? If you suspect the 2x pumps are too much for the FPR can you disable one of the pumps and test in low boost? A single 400lph should be enough for some low end testing. Maybe it’s not enough return line for that much fuel volume?
Just running 87 octane and the injectors are 210lbs. Main feed is 10an and return is 8an line, I can set the second one to come on at a higher rpm.