This one is new for me, taking it to the collective brain trust!

'84 Manual with a newly installed 2.2l GoWesty. Runs fine in all normal
driving conditions. When heading up a pass for camping this weekend, think
Western NC, couple thousand feet elevation over 4 miles or so.  The van was
under moderately heavy load in 3rd gear, RPMs on the high side but nothing
outrageous, was holding steady in power.

About 4 mins in the power hiccups slightly then continues on. I had a bit
of a corner so tapped the brakes lightly and find no pressure. Really
weird.  Made it to the top for a short flat and found I had to pump brakes
to get pressure.  This was short lived for a single application. As soon as
I let off back to no pressure, had to pump again. Then back up the next
section of the cut under similar load and had the same stumble at about
3-4min in then carries on fine. Top of that cut and the end of our trip out
the van is running fine, though a bit hot as expected, but no brakes
without pumping.

Parked,  camped,  had a great time celebrating or 4th wedding anniversary.
 (Someday I'll show you all or vanagon wedding pics, you'll like them)
Anyway, leave Sunday and brakes are fine, engine is fine.

What do you think? Related? Coincidence? Vacuum line or booster? Fuel
pressure or pump?

Thanks for any ideas, i try to keep stopping at the top of my list of
fixes!

Ryan
Asheville,  NC