Just a couple of thoughts. You still have a fuel starving problem with no idea as to why. I have to agree that changing the engine will solve nothing,since your not getting the proper amount of fuel delivery.
Check/replace the schrader valve in the fuel filter housing. A strong fuel pump (either type) and weak spring on the schrader valve will stop the flow of fuel in a heartbeat.
Harbor Freight sells a cheap,as in under 7 bucks hand suction pump. This thing will suck the hub caps off a 57 Chevy. Hook it up to the feed line going to your pump and see how "easy" it is to draw fuel into the pump. If it draws a vacuum and almost no fuel is being drawn into the hand pump you know for certain you have a plug somewhere.
If this happens,reverse the fuel lines on the hand pump and force fuel backwards towards the tank. You may free up the plug/clog.
I used this hand pump to find an air leak in the on-board generator's 16 foot fuel line. It turned out to be hidden on the back side of a hose clamp.
Do you have the original or aftermarket water/fuel separator? The original has to be one of the worst ever fielded. A sweat sock in a beer can.
These things leak air like a sieve when they go bad,and it will go bad.
If you have an aftermarket F/W Sep, fire up the engine and look to see if you have air bubbles forming due to a vacuum leak.
I put in a Racor Diesel F/W Separator. Not cheap,but first rate.
Just a couple of ideas.
