Did you use a pressure supply pump or just connect a pipe from the HP pump into a can of fuel.

Can't you T in a vacuum gauge into your test rig to see what readings you have then compare to that of the car.

When you have a different reading, work back through the pipework and connections to see if you have any leaks. Not sure if its possible but can you pressurise the fuel pipes to see if they leak.

I've done this with a hand primer on a Vauxhall Astra (accidently i must admit) by putting the primer back to front by mistake but this actually shown a pin hole in the pipe quite easily even though the van run with difficult starting fault.

I back fed the fuel filter if this is possible.