Thanks for your help, everyone, with my problems related to losing power
after 20 to 30 minutes on the road.  I disengaged the O2 sensor and it
doesn't seem to have a problem anymore, though it's smelling like it's not
putting enough air in the ignition chambers.  Oh well, should be a fairly
inexpensive part, and it's somewhere where I can get to it easily. ;)

Thanks again for your help diagnosing!

-Kyle Hamilton
'85 4-speed water-cooled Vanagon