Fuel Issue...But what?

[Dubv]

My '84 Eagle Wagon is giving me another hard to pinpoint issue.  258, auto.
The problem initially presented itself as a bad fuel pump, so I replaced it, car ran well for a bit, and now it seems to be having issues again.  It will occasionally die while driving, and then checking the fuel lines, they are dry between the pump and the tank.  I've also replaced both of the filters, so those are brand new.  The old ones didn't seem that dirty either.
Is there anything that comes loose in the tank and can block the sending unit?  I end up blowing in the fuel line back into the tank and it eventually clears out, and then gets back pressure and spits out gas again, I hook up the hose and its back running.

So, new fuel pump, new fuel filters...what could be going on in the tank?  Any other ideas of things to look for?

[AMC of Houston]

Could be a clogged tank sock, or clogged-with-rust hard fuel line.   Also could easily be a punk new fuel pump.  My own personal experience leads me to believe that about 25% of new 258 fuel pumps are no good right out of the box (work at first, then quickly fail).   Fill up the carb, put a vac gauge on the pump inlet, and see if you get any vacuum reading while running.  No or low vacuum = punk pump.

[Dubv]

Good ideas...I neglected to mention I first replaced the fuel pump maybe 3-4 months ago...thought I had noticed some lag so I thought "well, new fuel pump is cheap insurance..."  Thats the one that went bad first.  So I'm on my second "new" fuel pump here....so certainly possible its another crummy one.

[MIPS]

You could have a rust issue inside the tank where debris is plugging the sock but there's something like a pinhole further up the pickup tube inside the tank, so as soon as the sock plugs it pulls vapor.

[AMC of Houston]

And I forgot to mention the popular cracked (and sucking air) rotten rubber hose between the tank and hard line.

[Dubv]

I'll check out the rubber lines back by the tank again.  What is the small metal cylindrical thing back there that almost looks like a tiny fuel filter back right near where the sending unit comes out of the tank?  One of the hoses looked swollen at the end on that, so I trimmed it back and reclamped it.  The car gets driven a lot...it serves as my daily driver a lot of the time.  The tank was dropped to replace the sending unit with the last 6-7 years...so its not as if it sits a lot.  But still very possible something is washing round in there.  Last time I had a shop drop the tank...it doesn't look to bad on the face of it to drop it and remove the sending unit.  Anything I should watch out for there?

[MIPS]

That is the rollover check valve and vapor separator. It's part of the sealed tank vapor controls system and doesn't return liquids to/from the front of the car. It just prevents the tank from draining into the charcoal canister if the car flips. They are known to rust out but are no longer made, so I think people just replace them with a Delorean rollover valve.