fuel pump issue?

[bomberbob]

My son's 16 valve jetta died on the highway, it got towed home. He is tired of messing with it so I am buying it. Can't pass up a half decent Mark II.
The issue: I was able to get it to run, but I pretty much had to double the VE maps. and megalog viewer still says some areas are running lean. He said he replaced the in tank fuel pump before, with a new one. He replaced the outside fuel pump, what I refer to as the "boost pump" with a used pump off of one of my cars. Pressure gauge on the fuel pressure regulator says 30 PSI.
I haven't had a chance to look at it yet, I have a VR6 all taken apart in my garage.
Question: if the in tank fuel pump fails, does the boost pump have enough suction to pull the fuel up from the tank, or will it just cavitate? I always thought the in tank pump was a low pressure, high volume pump that just needs to push it up to the high pressure pump. I see potential problems as pumps, the fuel filter, the sock or whatever filter is on the in tank pump, blocked or kinked fuel lines, and probably a messed up pressure regulator.
Flow is restricted in some way, and the system is trying to open the injectors up twice as long to get enough fuel. Is there anything I am missing here?

[Prof315]

I'd look at the used fuel pump first. It is the "pressure" pump.

[bomberbob]

What if I decide to just replace the old antique fuel pump stuff with a Walbro or something like that? I did a search and saw some people had done that, but no specifics on how they set it up.
Does a Walbro 255 output bypass the boost pump, accumulator, and all that stuff and go straight to the pressure regulator up front (with a filter in there somewhere)? Use the existing plastic fuel line, or run a hard line or something from front to back? If prices were not so steep I would replace with VW components but sticker shock is pretty harsh on these parts.

[bonesaw]

I'd consider stock mk3 tank, pump, and lined.