Dose this car have power brakes?
What are the odds of a dying fuel pump, maybe just fuel starved when engine is warm and choke is open all the way?
A dying fuel pump will let an engine idle all day long, but as soon as a good load is placed on engine such as passing a car, accelerating up a hill its low output will starve the engine of fuel, and it will stumble falling flat on its face.
An intermittent skip from the same cylinder can be poor spark delivery, some kind of valve problem where valve won’t full close in a timely manner, or vacuum leak. It’s time to perform a compression test and stop chasing your tail. The suspense is killing us out here in slant land. LOL
You have a vacuum gage, now invest in two more necessary tools; a compression tester, and timing light. These simple diagnostic tools will make slanted life much easier.
