^^ just to clarify, the cheapest route is adding a 2nd box w/ native gears, so (stock) it's only 1-1, 1-2.3, 2.3-1, or 2.3-2.3. However alot of folks go ahead and havet he 2nd box regared for 4.7s so teh total reduction can be super low.

Somebody correct me if I'm wrong, but one more advantage for dual cases (over auto) is that you can get low-range (well 2.3x anyway) in 2wheel (rear) drive.
This can be nice if you have front AND rear lockers, often teh rear locker alone does the job, and by leaving the front disengaged it makes steering easier (b/c steering w/ a front locker engaged can be a real bear).

I *believe* there is a way to wire in a switch to similarly do 2-lo w/ the A340H auto tranny too.