Hey, last year I was a lousy climber, usually last or second to last in my group. Now am even and ahead of the guys riding a triple! Two things I did: one lose weight, I think it helped, second I sprinted up every hill and still do. Slowly at first some days they would be guys passing me on their big ring. I kept at it now I can make it up the hills on my big ring too. So find a hill and sprint up it 5 times twice a week. Before you know it you'll be in much better shape and the hills won't be as hard.
I am doing Levi's Gran Fondo as well I'll be wearing my 50+ kit. See you up there - Phil