As others have mentioned, fuel problem. If the truck has set for a while the tank could easily have crud in it clogging the fuel line. When it is under load it will eventually clog enough to stall. Then it sits for a few minutes and will start up because the pressure has released the crud from the line allowing fuel to refill the carb. Clean the tank, blow out all the lines, put in a filter before the pump and another before the carb and try again.

Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
“I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!
USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)