We have a 2014 Ford Territory petrol that has started hunting when climbing a gradual slope when on cruise control. It changes down a gear, revs higher, then changes back up again immediately and keeps doing this at approximately half-second intervals. It has only started this recently and does it consistently in D or S mode.
Have you heard of this issue before?
It could be the lock-up convertor locking and unlocking if you are driving at the point of lock-up. Try changing your speed up or down and see if that affects it.