Bad Condenser will cause that exact problem,
Replace that and you should be good to go.
You could try running it on carb cleaner first
and see if it does the same thing, probably condenser
Let me know what happens.
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Get a can of carburator cleaner.
When the truck starts to die spray
some cleaner down the carb and see
is it will stay running on the cleaner.
You need to establish if it is a fuel problem.
If it stays running on the cleaner then you
have a fuel problem.
If not you need to look elsewhere for a problem.
Trying this first was mentioned in my answer before
it was interrupted.
Brake cleaner will lock your lungs right up.
I tried on a car 20 years ago and almost died.
Never done it again!!
I be back in a little while.
I see you have the vacuum lock off.
You can bypass the lock off and just run
it off the convertor.
The lock off is only a requirement for indoor use,
for testing purposes you can bypass it.
You should be able to see how that is done.
It is just a matter of removing it and putting the hose
on the converter.
I have rebuilt more than a few convertors, I have come to
my own conclusion on a few of them there seamed to have cracking
in the convertor and it was hit or miss with rebuilding.
I always had a test converter on hand.
Bypass the lock off and see what happens.