I know alot of people hold stock by cross-training and/or working on specific muscle groups with specific exercises... so I am sorry if I bug anyone with this post...

But the way to get better/stronger at/on hills is to ride hills... at various intensities, repetitions, tempos... but ride hills.

How many hours do you think elite pro-riders spend in the gym working on their glutes? They know riding the course you want to be strong in is the best way to become strong in that discipline...