I have an ongoing issue with my 2007 Cadillac DTS. Whenever I have the cruise set (no matter the speed, but mostly at 60mph or 70mph) the RPM revs up and then drops back down - it does this randomly with no rhyme or reason. Does it on hills, straight stretches, etc. Seems like it might be a little more of a problem when I first get on the road - but even after a day of stop/go, will still do it. When I asked my service technician about it, he said it would do that when the filter was dirty. Well, guess what? After changing filter it still does the same thing. I'm not a car person, so I don't know if I've used the right terminology to explain the problem. Hope someone can help.