Alison makes 2 speed rear ends. You can not shift them when driving like you want and would give the the best of both worlds.
A couple of companies make a 2 speed gear box that bolts tot he back of transmissions. I don't know how they would work with autos, but I had one on my 68 C10 3 speed on the column and loved it.
Last I read the major manufacturers were only going to offer autos in there HD lines. I don't see them making anything over a 6 speed auto because of size. I could see a 8 or 10 speed if the made split shifts.
Size wise on a manual would also be huge at 9 or 10 speeds unless it was a split shift.
