Well, I finally got them off. I started gently, but it seemed to be having no effect. I gradually hit them harder and harder, until I started noticing a few little chunks of rubber coming off my mallet. I finally got a small block of wood, put the wood on the side of the caps, and hit the wood. It took some time, but I worked them all free. I hope I didn't cause any damage doing it that way, but they seem to look OK (to my un-trained eye). My book just said to "lift them off". Yeah, right!

Thanks for everyone's help - I couldn't have done it with out you all.