I had this issue once; whining fuel pump.  Horrible performance at higher elevations and higher ambient temperatures.  Totally ruined a Colorado trip in summer.  Dennis H. immediately diagnosed.  Replaced fuel tank.  All good.
But.....now just spitballing here, pure conjecture....what about removing screen on outlet of fuel tank and adding a pre-fuel-pump filter?  Why did VW put this screen into Fuel Tank?  I guess they never thought these bricks would be running over 30+ years.
I mean of course you don't want rust and crud traveling downline to injectors, causing even more misery.  In my understanding on my 85, they used a little clear plastic filter prior to the fuel pump, but I thought this was mostly to trap stuff following assembly of vehicle.  VW later deleted this pre-filter.
Just wondering your thoughts and experience.  A Facebook Vanagon Owner recently posted of whining fuel pump.  Not that I would be brave enough to tackle removing the fuel tank outlet screen; no problems now, no need to attempt, probably won't be for another 30 years.  But just thinking through the scenarios.
Rich
San Diego