What is Large Control Box Under Center of Bed

I was greasing my drive shafts last night on my 2013 DCLB 4x4 and noticed a large black box under the center of the bed. It's roughly 10"x3"x6". I can't find in on any electrical schematic. Anyone know what it is?

 

have a pic of it?

 

The only "black box" that size under the bed would be the Charcoal canister, that is kinda above the axle, towards the rear of the gas tank, right up against the bottom of the bed. No electrical there, just fuel lines. Unless some add-on thing

 

That makes perfect sense. I assumed I saw wires going into it, but the view was mostly blocked, so it must have just been gas/air lines.
Thanks!!