Not sure but worth a look see. How are your breaks? Speed control sensors, at least in previous cars, can be affected if the breaks are worn. I've never done research on my Xfire Cruise system before but I know in some vehicles the cruize can be affected by this.

Also, don't assume your battery is OK just because it checks out. Lot's on here about people who have don that and under load, it doesn't check out so well.

Good luck. I love the cruise on my car. It holds speed very well, even on grades and it sure helps to keep me from going too fast