If it's P0446 just reset it and see how often it comes back. Make sure the gas cap is on tight and clicks like it should.
Mine does that and I've narrowed it down to when I refuel on an almost empty tank and only put a few gallons in it. Then the next day or so I get that code. As long as I fill it up each time I don't see it at all. I just reset it when it pops up.
EVAP codes can be tough to nail down. I wouldn't worry unless you start smelling gas inside the truck.