[tonytone]

Hmmm, that's interesting; IIRC on the OBS GM fullsize SUV/trucks, the owners manual states that Auto4WD can be used when the pavement isn't dry (e.g., wet conditions) but not highly recommended when the road is dry...but perhaps the Autotrac has been changed with the NBS vehicles.

I do know that at least in '03, GM offered a full-time 4WD option (not the same one as the AWD found on the Denali--the primary distinction between the two is that the full-time 4WD option has 4LO; neither option has a 4HI button, BTW) that eliminated the need for the Auto4WD button offered in the Autotrac 4WD option found in GM full-sized SUV/trucks, so I reckon it would make no sense for GM to offer that Auto4WD can be used all the time (i.e., wet and dry roads) if they have a fulltime 4WD transfer case option available which can be used on both wet and dry pavement...not that you can force the full-time 4WD to operate in 2WD mode.