Marcus,

Dropping the tank might be worthwhile anyway, but you told me privately
that your repair guy already pointed out a problem with the wiring to
the coolant temp. sensor.  Personally, I spent nearly $1000 (yes, 3
zeros), replacing fuel related components before tracking down the
problem to that sensor.  One mechanic even told me that it was my tank
and that it should be replaced.  My symptoms were:  drove for about an
hour great, then would start backfiring, kicking, bucking;  max speed
would steadily dwindle til I was on the side of the road.  Would sound
ok til it hit around 3000 rpm, then backfire back down to around 2500.
This continuous surge/die continually worsened.  Couldn't resume normal
operation until it completely cooled off, then it was perfect again.

On cooler days, I might be able to go a little more than an hour,
warmer, less.  Despite my many attempts to convince my mechanics that I
thought it was temperature related, they insisted that it was a fuel
problem.

If you haven't corrected that wiring yet (and possibly replaced the
sensor), I'd recommend doing that first before fooling with the tank.
Even if it is the tank, that wiring problem with continue to cause
problems.  IMHO, its best to attack the obvious before going into the
unknown.

That sensor cured my problem for the last year, so in my case at least,
it wasn't the tank.

Good luck,
Tonya
87 Vanagon GL Wolfs
74 S. Beetle