Dave
I'm sure you got a real good look and know what you saw, but is it a possibility that you could've had a black bobcat out there. They are in your area as well as mine.
Ooops, you said it wasn't a bobcat. Sorry.
My BFF is from Jacksonville and said that her mother claimed to see a 'black panther' on several occasions as she was growing up. She said they would set out traps but never got any thing.