I would start by checking the fuel pressure. Start with the gas filter then disconnect the fuel line before the external fuel pump. Use a metal can like a coffee can. Have somebody else try to start the truck just make sure the primer pump is working.
http://www.autopart.com/tools/toolsmain/tool/T_3440.htm This is a picture of a pressure tester. If slightly low check the vacuum hose for the pressure regulator. If you find gas replace it otherwise pinch off the return hose if the pressure is satisfactory at this point replace the regulator.
Some of the newer units have a damper instead of a pressure regulator. The control pump voltage by cycling the fuel pump ground and have a pressure switch. Make sure what you have before changing parts.
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