Yeah, with cruse on it will automatically downshift for you going down grades to help maintain your set cruising speed. Just like it does when you tap the break petal while descending a hill in tow/haul mode.
However, going up the grade with the cruse set in tow haul mode makes it keep dropping gears to maintain your set speed plus some it seems. I only know this from the times a hill or grade "sneaks" up on me as the coach pretty much drives itself with cruse set.
2011 Sunseeker 3170DS - 30,000 miles explored