Differential Unit problems of the 2005 GMC Canyon

I have a 2005 GMC Canyon 4wd cc p/u . This p/u was purchased new in may 2005. The window sticker clearly lists an auto locking differential under standard equipment. In November 2005 GMC sent a letter to me which stated that this vehicle does not have a auto locking differential. As of this date (2-2-06) GMC admits that the window sticker is wrong, but other options were added to make up the difference. I don't know how this could have been done. GMC also is not willing to do anything to correct this mistake made by them.

While driving approximately 40 mph, the front wheels inadvertently locked. This caused the vehicle to spin. The pan on the front diffrential hangs down 1/8 inch and the diffrential oil leaks out.