[BrianR]

OK Professional opinion here.

Do NOT use your cruise in the rain. You can easily hydroplane and when you do, the car will slow down a bit. That's exactly the wrong time to apply power, which is just what the CC will do, causing you to spin out and lose control. I do not use my CC in the rain, snow or heavy traffic and neither should anyone else. It probably tells you that in your owners manual.

Mountains are a different story as my CC is a bit different than yours. If your actual speed drops more than ten mph or so from your set speed, the CC will drop offline to allow you to take more appropriate action, such as gearing down. My truck will NOT drop offline however. It keeps the power on no matter how much I slow down so that when I crest the hill, I can go right back up to my set speed again. Just in time for the next hill. ETC.

And just for your information, the cruise control unit takes it's data from vacuum and magnetic sensors, not the speedometer. Go to How Stuff Works website to see more info. I'd include the link but Quick Reply doesn't let me, and I'm too lazy to type in the proper codes.

Brian