+1 for this problem. Looks like it could be a common problem, my car does exactly as described.
It's as if the car 'forgets' to accelerate as it goes up the hill. It doesn't even seem try to accelerate as the boost guage does not move.
However, when I feel the car not accelerate, I can give it a little right foot and the car 'remembers' to accelerate again and the cruise control does not cancel.
Happens about 2-3 times between Sydney & Canberra. Service people told me the car will cancel cruise if the speed drops too much and could not replicate the problem. eh..