I just discovered this thread, and I have to say I give you major credit for dealing with him for this long! He sounds downright terrifying. I'm really glad that you made some progress, too. Congratulations!
As an aside... I -love- pitbulls. They are absolutely gorgeous, and really intelligent dogs. We've had several in the past. If you get them from a responsible breeder, they're amazing with children, and don't have a mean bone in their bodies. Yes, they are bred to be vicious fighting dogs in many areas of the country. But Pit Bulls themselves as a breed aren't terrible... just the junkyard/fighting bred dogs. For them, there is no hope... agression is bred (and beaten) into their genes for generations. There are plenty of wonderful pit bull breeders in this country trying to promote the breed as wonderful pets, no aggression at all