Cruise control quits going downhill

[BigBL87]

I have a 99 Grand Prix GT, no mods. I'll be driving home on the interstate w/ cruise on n start goin down a hill (doesn't need to be very steep) and my cruise control will shut off. Before it shuts of, i can feel the car shake a little, like its tryin to brake but not workin. I'll turn it off n reset it, and it works just fine. It's not a huge problem n I can live without my cruise working, but it does get pretty annoying. Any ideas or suggestions? Thanks.

O, and I have virtually no mechanical experience, can't do much to my car except change the oil. I'm just lookin for an idea of what it might be.

[Chazman]

Cruise control does not have control of the brakes.
It will however, allow the motor to idle down when once your speed passes the set speed, like going downhill.