Is it returning a significant amount of fuel? If returning fuel it is getting through adapter or relief valve without building pressure, if little or no return, the transfer pump may be weak.
I can't remember the exact details, but there was an "upgrade" kit available to a different pressure relief valve, raised fuel rail pressure, IIRC?
You mention having the transfer pump "rebuilt", what was done, new gear/shaft to seal it up? Really nothing else that could be done if the housing is worn?