Heeeeeeeeelp!

I am pulling my hair out trying to solve an ignition miss on my '88 GL. 
When it happens, the engine is warmed up and I'm usually just cruising
along.  The engine stutters and the tach dips and even goes up a bit
sometimes.  The fuel pump is good, quiet, filter is about 2 months old. 

Initially I suspected it needed and tune up and have replaced the plugs,
cap, rotor, and wires using the appropriate parts from Bosch.  The
problem persisted so I replaced the ignition switch with a new one.

The problem persisted... reading up on the symptoms I thought it might
be "vanagon syndrome" so I swapped in a different AFM, still there. 
Added the proper capacitor to the AFM innards, still there.  Unplugged
the O2 sensor... still there.

Any ideas?  Does the hall sender in the distributor do this when it's
failing?  I think it's more of an on/off failure so I'm stumped.  Thanks
in advance.

Gregory Smith
'88 Vanagon GL
'77 Lancia Scorpion
Olympia, WA