Wow I sold a used one for more than that a year ago. Worked really well on the old truck, IIRC I got 18 USmpg hand calculated on a ski trip from edm to sunshine, winter fuel, 130 k the whole way. I was pleased.
I would have no problem using it on the Tow setting, and on perfoemance you'll be fine too. The thing to keep in mind is that the hardest shifts for your tranny to make are the high gears - so don't hold it wide open when it's shifting into 5th and you'll probably never limp the trans.
Something to keep in mind, the Extreme setting has enough nuts to hurt your tranny if you abuse it, but if you drive normal, you might get your best mileage on the highest setting. I think I had the best luck on Performance though.