The Big Tow would mean your truck came with a hitch receiver..... 
Seriously, the Big Tow comes with the 3:10 gears (not that you'd notice by looking at the truck), a "Tow Mode" button on the center console under the heater controls, and the most obvious feature, the Big Tow extendable mirrors.
And I don't know that I've seen a published figure for "towing capacity" of a non-Big Tow Titan.....
Seriously, the Big Tow comes with the 3:10 gears (not that you'd notice by looking at the truck), a "Tow Mode" button on the center console under the heater controls, and the most obvious feature, the Big Tow extendable mirrors.
And I don't know that I've seen a published figure for "towing capacity" of a non-Big Tow Titan.....