I suck at hillls too. I am not embarassed at all to shift into the granny gear and just pedal really, really slow. I have had recent breathing issues which I can relate to allergies.

The only way to get better at hills is to ride hills. I'm not sure about spinning class techniques. However when I ride my bike on a trainer I often switch to a harder gear in increments of 5 minutes, which is sort of a simulated hill.

Good luck