The cruise on my "new to me" '00 2500 24V doesn't like the stay at a set RPM after you set the cruise. I'll set the cruise at a speed no problem and it will keep the speed for awhile, but then it will rev down and speed down. Then it will rev back up and speed up to the set speed. It does this over and over again, until I shut the cruise off. Wondering if you guys know whats going on and what I'll have to do to it to fix it.