The transmission may downshift on hills to maintain the vehicle set speed.
The Cruise Control system maintains speed up and down hills. A slight speed change on moderate hills is normal. On steep hills, a greater speed loss or gain may occur so it may be preferable to drive without Cruise Control.
Cruise Control can be dangerous where the system cannot maintain a constant speed. Your vehicle could go too fast for the conditions, and you could lose control and have an accident. Do not use Cruise Control in heavy traffic or on roads that are winding, icy, snow-covered or slippery.