Cruise control

I have a 98 durango and when i push the cruise button on the wheel the cruise light comes on but it doesn't stay at the speed that I want it to stay at.

I also have the same problem. I put an OBD2 reader on it, and it returns no code. At times, mine won't come on, or it will not accept a speed-- I had the switch replaced, but no help. I was told by the dealership to go directly to the dealership when this happened, and not to shut the car off or mess with the cruise - they want to try their diagnostic reader.
Most of the time it works fine; sometimes after shutting the car down a couple of times, it starts working again.