99 vw loss of power...tried everything...please help

I have a 99 vw gasolined powered gof that has an intermittent misfire,
hesitaition, loss of power problem. It has pretty much always misfired
but my main concern is the new (past 6 months) hesitiation/loss of
power. It will completely die unexpectedly and then after a few
seconds to a few minutes, it will restart. You can floor it and the
tach barely moves and then it may suddenly grab and you're off! The
problem is beginning to get much worse. Here is a list of what has
already been done:

New:
MAS
Gas Filter
Catalytic convertor
throttle plate
wires, plugs, cap, rotor
coil

The vacuum lines, fuel pump pressure, and regulator have all checked
out alright. The gas tank was drained and is clean. The fuel injector
lines have been cleaned twice.
I wanted to change relay 109 untl I realized that that was only for
diesels (I think)
and now want to change the relay for the fuel pump (#409) but I don't
know where it's located (it's not in the panel)
Most of the time the problem happens when the gas level is below half a
tank and it will even repeatedly hesitiate going up a steep hill when
it's below half a tank but not when full.

Any thoughts/suggestions...if yousolve it I will take you out to
dinner...as long as you're not a jerk!!!!! Thanks. Andrea