I went on the live chat on the GMC website and asked when the 2016's will be available to order and if they will have an 8 speed transmission. This was the response I got:
Me [2:53 PM]: Hi Melissa, do you know when 2016 Yukon SLT's will be available to order and if they will have the 8 speed transmission?
Melissa [2:55 PM]: Thanks for your interest in the Yukon! As of right now the approximate date for the 2016 model is 07/20/2015 in Arlington, TX. Just a moment while check to see if we have information available yet for the mechanical specifications.
Me [2:55 PM]: Okay, thank you!
Melissa [2:57 PM]: You're welcome! I'd also recommend keeping in touch with your local GMC dealerships for information on when they'll be able to begin ordering these models. Would you like the contact information for dealerships in your area?
Me [2:57 PM]: That's okay, I have their information
Melissa [2:58 PM]: Okay great! Do you have any other questions about the Yukon while you're here?
Me [2:58 PM]: Were you able to find out the mechanical specifications for the 2016 model?
Melissa [2:59 PM]: Oh I apologize; no, we don't have that information available just yet. You may wish to keep an eye on
www.media.gm.com for updates on this vehicle.
Melissa [2:59 PM]:
http://www.media.gm.com
Melissa [2:59 PM]:
http://media.gm.com/media/us/en/gm/news.html