I've had the same thing happen on two different Nissan's I've had when I let the tank get really low and then filled it to the neck. Recently it happened on my Dakota (when I left the cap off) The check engine light lit and the manual indicated it was an emission issue that brings in the light usually related to the gas cap. It's probably the same type of issue with your truck. The manual said it should clear after a few engine run cycles and if not, go to the dealer. It cleared on the Nissans after about 5 run cycles and the Dakota after about 10. I say run it and see if it clears though, if under warranty the dealer will just check the code, check for any other problems and probably just clear it for you. You may never see it again.