85 gmc p/u cutting out under load

[Dia]

Hello,
This is my first visit to this forum. I am glad you are here.
I have a question.
When we drive up hill, the truck it cuts out badly. It started slowly, seeming like it was not getting fuel, but now it is getting very bad, so we can barely drive even on a flat road.
It is now parked and I am getting ready to look at the carb, fuel filter, etc. I am wondering if someone could tell me a good order of approach to diagnosing the problem.
I wonder if the fuel pump could be giving out, or if I have a clogged jet, etc, so I would like advice on running through all these systems in logical order.
Greatly appreciate all help and advice!
Dia