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Any junction point in the fuel line from the tank to the fuel filter should be a prime suspect. You can get a handheld vacuum pump (mity-vac comes to mind) and create a vacuum at the fuel filter inlet - coming from the tank - and pull this with the vacuum and see if you get fuel. The amount of vacuum created by the truck's CP3 is pretty low and could be replicated with the handheld vacuum pump. If that fails, there's a junction point in the fuel supply line over the driver's side valve cover, so try there, and keep on going until you get to the tank. If your CP3 won't pull the fuel and the fuel filter primer won't pull the fuel, something's not right. Pretty hard to guess exactly where and what the problem is unless the truck is present.

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You could put a clear line at the fuel filter head and see what that shows you, air bubbles, some fuel, no fuel, etc. while the engine is cranking. You could also test the vacuum by using the test port on the inlet side of the engine, looks like an air conditioning valve/port.
 
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