Cruse Control, software problem???

Hello - I have a 2004 Envoy XUV. If I am using cruse control during a long assent and the trans kicks down into a lower gear, when I reach the crest of the hill and drive for several miles, I notice the trans has not "reset" or up shifted to the appropriate gear. Once in this mode, it will stay in that gear until I tap the brakes to clear cruse.