Do these have the filter in the fuel inlet to the carb?
If so might be worth checking.
Get a spray bottle, throw some fuel in it and spray it down the carb whilst cranking it over. If it fires up you know you have a fuel issue. If not, probably spark.
Also, long shot but worth a consideration. Check the fuel tank hasn't got a bit of paper or bottle label in it which could be blocking the fuel pick up intermittently and causing a drop in fuel pressure and therefore performance and starting etc.
Had exactly this problem in a Ford Capri I purchased for cheap because the previous owner got fed up with it breaking down.
Always seemed to happen when the tank got below 1/3. Complete fluke but found the label to a can of STP in the tank on the 3rd time of taking it out.
Removed label and car fixed.
Keep diagnosing it and you will get there PLUS! you will know your truck inside out and be able to fix any fault at the side of the road in the future!
P.
