I wasn't able to find this information anywhere, so I thought I would go ahead and post it in case any one else needs it.
If you have the Sierra Multipro or Silverado Multi-Flex (Multifunction) tailgate (RPO Code QT5) and don't have power to the truck, there is no way to open the tailgate.
It's actually pretty easy to open it. You just need to disconnect the connector for the tailgate under the bed, and you can manually power the latches. I attached the connector end view diagram to this post. On the diagram, its the left connecter at the top of the first page.
If you want to open the main tailgate, apply 12V to Pin 30 (Green) and Ground to Pin 17 (Yellow with Black Stripe) and it will open the latches.
If you want to open the inner/upper tailgate, apply 12V to 16 (Violet) and Ground to Pin 18 (Brown with Black Stripe) and it will open the inner tailgate.
I use a portable jump box as the power source and paperclips in the connect pins. I use a set of test leads with alligator clips from the paper clips to the jump box leads.
Hopefully this helps someone else.