I don't see where the six speed auto is standard on the Tahoe. I know it's available if you get the LTZ with the 6.2, but unless I'm mis-reading the list I don't see the six speed auto offered with the 4.8 or 5.3.
But standard six speed automatic on the Avalanche, half ton Suburban, and at least some of the trucks is a good move.
GM should have the six speed autos across the board just in time for the competition to start making them obsolete with more dual electronic clutch transmissions (like in some Audi models, and in the upcoming Ford Powershift transmissions).
But at least the four speeds are really starting to disappear.