I am always getting passed or dropped on hills. At first I blamed it on my bike, wider tires, smaller wheels, heavier. (the bike not me)
Then I graduated to a road bike, smaller tires, bigger wheels, lighter. (not me - the bike - I gained a few pounds so we are now about even again
I was still getting passed.
I went to the doctor "Dr, Dr, what can I do ? ? I can't breathe when I climb hills,please make my lungs better - I want to be able to climb a hill without dying"
Lots of tests later I discovered I was functioning on 65% lung capacity and was chronic asthmatic (I used to just be exercised induced). Very expensive medicine later my lungs are much better although still not perfect