I completed a hilly century event this weekend, the event had several 13 to 19% grades. At 215 lbs, this was a challenge.
Keeping my speed down while climbing helped me finish the event. After a little trial and error, I could travel at 4 to 5 mph with a 50 rpm cadence. This worked much better than trying to hammer up the hills at 8 mph.
What is your climbing speed and cadence when the hills are steep?