I have an '84 with this drivetrain, too.  (Soon to be remedied....)
I've wrapped mine out to the 6500 redline, according to the tach in the
dash, though it often won't rev that high, even in first, when I get very
far into the hills around here.  As for going downhill, I try to keep mine
below the shady reline (6000).  I've never had trouble with the
transmission overheating, but, I run Amzoil in it.

Mark in Westminster, CO

BTW, I have a 3 speed automatic 1.9L and I just ordered a tach to
monitor the engine when I charge up and down steep hills in
mountainous campgrounds.  When I'm going up steep hills in 1st or 2nd
gears, what RPM should I keep the engine at?  I'm talking about hills
that I go over at a max of 30mph with the accelerator floored, usually
cruising in the 20mph to 25mph range with the van working really hard.
  Same question for going downhill.  I burned out a transmission going
down a dirt road in low gear a couple of years ago and got stranded in
a town of 75 people during the opening weekend of duck hunting season.
 (I don't hunt).