started my truck today and engine light came on throwing a P0456 EVAP Emission Control System Leak Very Small.
any ideas? i checked the gas cap and it seemed tight. the truck has had a cold start for months im not sure if this is related.

 

Could be loose or cracked filler hose(from gas cap to tank).

 

Could the charcoal canister be plugged? I once read where the F150's had an issue with folks over filling their gas tank; instead of stopping the fill-up when the nozzle shut off, folks would squeeze the handle a couple of more times. This would cause raw gas to drain down the overflow tube, intended to capture the gas fumes into the charcoal canister, and then get re-burned by routing these fumes to the intake manifold. This canister gets clogged with the raw fuel from over filling, and was setting a code.

Is this the same?

 

Double check for cracked o-rings on the gas cap. Just because it is tight doesn't mean there isn't a small leak still. Mine had the main o-ring seal cracked in various places but not all the way through. I replaced the cap, reset the light and no more code.