I'd say either avoid such steep hills for now, practice and get stronger on lesser (but not too easy) hills until you can confidently ascend that tough one; or, try the pedals with SPD clipless on one side and conventional platform pedal without any attachment on the other side, until your fitness improves where you can take any hill without fear of a stall-out. In the meantime, on your rides, be sure that you are practicing climbing out of the saddle so that your legs, heart and lungs get built up for doing more work and dealing with the pain. I suggest you train your body to the point where just about any hill can be taken sitting down, while using stand-up power to get you thru the steeper sections, to just change position on a tough climb, or to surge away from a mad dog while right in the middle of a steep ascent. Good luck.