I don't have a '17 ... but ... Gear down ... If you set cruise at about -5 the speed you want, it'll do the down shifting for you and keep you nicely at about +5mph the set point. Otherwise you can do it yourself with the tow-haul button and it'll downshift when you touch the brake. Don't be afraid to move that gear shift lever to downshift manually
Downhill = down the speed to keep yourself and those around you safe.