Some short and sweet advice for you…
1. Maintain the successful rhythm you have established on the flat.
2. Maintain the SAME EFFORT LEVEL, same breathing ; if you keep up the same pace on the hills as on the flats, you’ll wear out!!
3. Shorten your stride and let yourself slow down gradually as you ascend ; conserve energy for the rest of the hills.
4. Pick up the rhythm slightly as you near the top. A slight increase in arm rhythm(swing) helps you do this.