I have a new gen. '16 Tacoma, 3.5, auto, 4x4. Towed my B & my G/F's Scout (right @ 2,000#), over 2600 miles, between 12.5 & 14.8 mpg. Nothing to brag on, Toyotas are not know for good mpg, my Tacoma gets 22.3-23.8 empty bed running around local. I understand it's the Toyota tranny 5 & 6 spd just don't get the mpg the other brands get.
My '06, V6 4.0 Tundra 5 spd auto, 4x2, got about the same towing mpg as my new one.