96 4.3 no fuel pressure

Had a leak in the lower intake gasket. Pulled intake all as one. Fuel rail was tough to get back into upper holes. Old O-rings still in this port. Got it all back together and can't hold any fuel pressure. Pump sounds OK. Can hold shrader valve open to get fuel to spew but won't hold enough pressure to start. I think the problem lies in the connection from fuel rail to upper intake. There isn't any gas leaking from there though. Do you think the filter could be THAT clogged to cause the problem? Do I have to take the upper off to replace the O-ring for the fuel rail? They are at the bottom to the port. I'd really hate to tear in again but I do have the rest of the gaskets from the kit.

Thanks.