What happens first?
Does the engine rev faster, and then the cruise control turns off?
Or does the cruise control shut off first, and then is followed by the high revving?
If its the first, where the engine revs faster, and then the cruise control turns off, is this happening when you are climbing a big hill?
Most cruise control systems will turn themselves off if the car climbs a hill, but loses 10 mph. So basically, as the car starts climbing the hill, it will first try to downshift into a lower gear, causing the high revving, but because the engine isn't powerful enough for this hill, the car drops from the 65 mph that you had the cruise set on, to 54 mph, and then the cruise control turns off.
There is no actual problem with the car in this instance, except that the car doesn't have enough power for the hill.