Nick
The dealer that takes delivery is supposed to an all points check when they come in, this would also include checking all fluid levels too, it most likely happened at your dealer, prolly some punk kid that has no pride in his work, I would check the whole truck from front to back if I were you, I would also go back to the dealer and ask to see a copy of that check list on your truck, maybe the dealer would get on the kid and it may not happen again.
There is a post up now that a fellow TDR buddie lost the rearend in his truck and it turns out it had NO OIL in it, it missed getting lubed at the factory and getting checked at the dealer.
Crap like this is why I prefer to do all my own work.
cheers, Kevin