Truck won't start after sitting for longer than a day

This can happen when the check valve in the fuel pump assembly leaks pressure back into the fuel tank. The longer the truck sits the harder it is to start. Try this, turn the key on for 2 seconds then off, do this two more times then try and start it. If it starts right up then the check valve is the problem. When the key is turned on the fuel pump only gets 2 seconds of power, so if the line pressure is at zero there isn't enough run time to pressurize the fuel system. Cycling the key a few times forces the pump to run for 6 seconds instead of just 2 and this will pressurize the system and allow for a quick start