cruise control problem

Everything about the cruise control works except: when going down hill, my 98 Tahoe does not brake. I can gain 10 mph or more on a good hill with the cruise control set. Any ideas?

Cruise controls don't brake, they only let off the gas. If you are going down a steep grade then any vehicle will pick up speed if it's big enough. Cars don't as they are usually lighter and the engine has enough compression to keep them from picking up speed. Larger SUV's have more weight and are more prone to picking up speed.