Mate you cant go wrong with the dmax, I have the 2014 model auto (same thing) and they just have got everything right! strong, reliable, great towing, heaps of torque/pulling power. Tritions are ok for what they are I guess but the dmax just ticks all the boxes and super reliable especially if you want to keep it a longtime. As for towing economy im not exactly sure as I haven't had a chance been to busy with work but you always hear good things from Isuzu not often you hear a bad comment. Go onto the 4wd action forum and check both utes out youll see what I mean.
Anway all the best with the decision.
J