I will admit, it made me laugh.

P0455
"EVAP Emission Control System Leak (Large)"

So what might it be that I'm overlooking... all I can think of is something with the charcoal canister, but all the lines are still attached.. that I can see..

 

Leaky gas cap, driving with the gas cap loose or off or some other vapor leak from the fuel tank system or from the evap lines.

 

wenzinger beat me to it, thats typically the gas cap. in newer model cars that code actually triggers a different light on the dash, a check fuel cap light.

 

Yup, Ford added the Check Fuel Cap light to cut down on bogus OBDII warranty claims caused by driver error when refueling. The Check Fuel Cap light comes on first when the Evap Monitor detects a gross evap leak. If the problem isn't corrected after two more 'trips', the computer assumes that it is a real evap leak and the CEL comes on. I believe that Bob is correct and 99's didn't have that light.

 

Wierd.. I haven't put gas in the truck in almost two weeks... better go check and see if somebody stole it.. lol..