Well no wonder I couldn't make it up that hill...

[OakLeaf]

I seem to lose all the strength in my legs right about then and have to spin slowly to get up.

So often that's a nutrition issue for me. When I'm out of glycogen I don't feel hungry at all, I just can't make power. (Although I wouldn't exactly describe what I'm doing up a 10%+ grade, when I have to take it slowly, as spinning. ) Just as you describe, when I call on my legs, there's nothing there.

I've started to put HEED in my bottles for every ride, and it makes an enormous difference. The "real food" alternative for me was to eat a big bowl of brown rice about three hours before the ride, which would keep me going for a hard 35 mile evening ride. On a morning ride, I just can't get up early enough to eat carbs that are complex enough to be in my system in time for the ride and keep me going throughout it.

[Crankin]

You know, Oakleaf, I think it could be a nutrition issue. I have recently found that I need to eat a Luna bar before even one of my short "after work/out of time" 15-18 mile rides, or I really feel like crap. Since all of my rides from home involve a mile climb at the end, I am spent after that. And yes, I rarely feel hungry on a ride, but if I don't eat a lot, I feel worse. My friends seem to exist on 1-2 bars and a pbj sandwich, with some type of sports drink on our 30-50 mile hilly rides, but I think I need to do more. I am wary of eating too many calories, but it's becoming more and more of a problem.
I still want to work on my strength, though. I can barely get myself to stand on my pedals, which is why I had to walk part of the 20% grade in Connecticut a couple of weeks ago. When the others stood for the last hard part, I gave up. And that's something I don't often do...