If you press select reverse, and hold the "M" button until you hear two beeps from your seat.
(This enables the auto dipping mirror function when reversing)
Or select reverse and press and hold the "M" button again to disable the auto dipping mirror function when reversing.
(This will sound 1 longish beep)
If it still doesnt auto dip, then you may need to set the mirror position when reverse is selected.
To do this,
1) Make sure that the Auto dip function is enabled
2) Place the transmission in reverse.
3) Set the position of the mirror to where you would like it dipped when reverse is selected
4) Press M and select a preset (1, 2, 3) that you would like to save the mirror position.
As for saving positions,
Each key has three memorys (Which are used for Mirror positions and drivers seat position).
To save your settings, Press the M button (Beep), and press a preset button (1, 2, 3) on the side of the seat to save your settings.
Also the radio/HVAC and some other settings are stored for each key.
So if you give your misses a key, then that key will change the seat position, mirror positions, reverse dipping option, HVAC Temps, Radio settings, and other settings as well).
Hope this helps.