Cruise Control problems of the 2006 Chevrolet Colorado

When using the cruise control on my 2006 Chevrolet Colorado, particularly when going downhill, the cruise control does not hold the set speed. Setting the cruise control at 55 mph and then going downhill, the vehicle will accelerate up to 64 or 65 mph. Obviously, to obey traffic laws, the brakes are applied and disengages the cruise control. However, when the cruise control is set at 65 mph, and goes down hill, the speed will only increase to only 67-68 mph. I have tried setting the cruise control at 55 mph on various roads going downhill, and the results are consistent. The speed of the vehicle will increase by 9 to 10 mph. When I first purchased the vehicle, general motors did contact me soliciting my feedback on the new vehicle. I did make the representative aware of the problem with the cruise control. I was also asked if I would be willing to talk to an engineer about the problem. I was agreeable to this, but was never contacted by gm. I had the cruise control checked by my dealer. The dealer found that the cruise control was working according to specifications. The vehicle was not tested under the same driving conditions that I experienced the problem. I have also sent a letter to gm Chevrolet customer assistance two weeks ago, in regard to the cruise control problem. As of this date, I have had no response. On a separate note, I have other Chevrolet pick-up trucks in the family and the cruise control holds the set speed going down the same hills that the cruise control fails on the 2006 Colorado. This problem has been occurring since January when I purchased the vehicle.