I only had a half-ton v6, but I almost always ran tow mode with it, especially on the highway. It keeps the convertor locked up tight to prevent heating (heat is an auto transmission's worst enemy) the transmission fluid. I could run 60-65 with a light throttle and it would never shift or unlock, if I kept my speed at 65 I could get 22-23MPG plus with it.
It must have changed the engine tune as well because it made that little engine feel a lot bigger, even at 70+ on the interstate.
It raises the shift points (upshifts later and downshifts earlier) so that it doesn't lug as much. So the worries that used to go along with towing in OD (mainly not pumping enough fluid at lower RPM to feed the transmission and circulate it through the cooler) are eliminated. A beneficial side effect of that is it also eliminates the hunting for the right gear.
I'm not sure (mine was a basic wt and had no cruise control) but I believe it may downshift going downhill to help hold back your speed as well.