Voila, 1450: Inability of Evaporative Emission Control System to Bleed Fuel Tank.
I cleared the code, we'll see if it decides to come back or not. If it sticks, it's most likely a check valve in the evap cannister, which, I'm guessing, I should be able to browbeat the dealer into replacing under warranty unless they throw a fitty about my exhaust and chip. (Chip won't be on the truck for any warranty work though, that's for sure.)