a $10 HF timing light you can check
static timing
mech adv. timing,
vac adv. timing.
ALLabove ok?
then back to carb.
your jets are dirty.
car is going lean.
all carbs, need to provide more fuel under more load.
(same with EFI ) { map or maf, as approp)
on a carb how this happens varies all over the map.
it takes little fuel to rev any engine with no load (you saw that)
and if going up hill , max.
usually it is 1st to 2nd gear power shifts up a hill , is worst case on all cars
I can prove that with my MAF data logger.
Carbs need to be boiled out (chem cleaned) and kitted every 100k.
I have no carb pages. (they are mostly dead here since 88)
http://carfix.stufftoread.com/