I am having the same problems right now.  I just put new heads and a new
air flow sensor on.  Same ok at low speed, cuts out at high speed.  Put a
new pressure regulator on and it was much better.  I'm still running rich
and will be dropping off the van tomorrow to get the afs setup tomorrow.
Sounds like you're running rich too.  I made my drive from Cleveland to
Boston without major mishaps but had to keep the speed down to 70 and
accelerate very slowly....

good luck,

-- John