You know, I rode with a mirror on my helmet for YEARS, and then one day it broke. After I got over the habit of always looking up at the now absent mirror to see what was coming up behind me as I rode my daily commute on very busy roads (hills included), I found cycling much more RELAXING without the mirror. And safer, too, because I was paying more attention to my own cycling and what was right in front of me rather than being distracted by my own fearful glances of what might be coming. From then on I always assumed that some driving asshole was coming up too fast on my butt, and I learned to find my solid, visible position on the road and ride it firm and steady. Really, vehicle drivers don't want your blood on their cars (cyclist blood can be so.... inconvenient), so try riding that hill with confidence. Good luck!