Simple question - is there a fuse/relay that I can pull to disconnect all power from battery to electrical system including onboard computer and any other drains when vehicle is off and key removed? THANK YOU IN ADVANCE.

Welcome to the forums John.
I just had a good look through the owners manual and there does not appear to be one single "delivery" or main fuse to pull. I wish I could be of more help.
Without a factory service manual at hand, I would probably recommend that you contact a dealer for further information & assistance.
One of our other members may have more information, or a FSM handy.
Alternatively, you could disconnect the battery cables.

Soft Ride, many thanks I went through the owners manual as well and thought I had it narrowed down to that fuse/relay.

I would be happy to contact my local dealer however currently OCONUS and 6 nautical miles off of Hadera, Israel until end of June which having my bride disconnect and reconnect battery terminals makes for a problem and drove me to a support website.

Tks b well, maybe someone in the group has a service manual or I might start another thread for that.

John as you are a service member, and I will be close to a dealer late tomorrow, I will stop by the service department, and see if I can find out the required information for you.

Soft Ride, although President Theodore Roosevelt called the US Merchant Marine "the fourth arm of defense" and I have worked for and with both the US Nave and Marine Corp we aren't service members per se such as the brave men and women who serve in our armed forces. With that being said so that there isn't any confusion as to my status, I am very much appreciative of your offer to speak to a service department AT YOUR CONVENIENCE. Thank you sir

Hello John, I stopped by the local dealer.
I asked the senior service mgr if by chance like most new vehicles, there may be a hidden delivery fuse.
This is so that the car can be transported with no electrical connection.
Once the vehicle is safely delivered ,the dealer then installs the fuse as part of the dealer preparation.
Only the newer vehicles have this feature and the 2002 Yukon Denali XL does not have a single source for disconnection.

Possibly your Bride (congratulations by the way) could connect a trickle charger until you get home as a thought.

Soft Ride, many thanks for your time and the good information. Trickle charger sounds perfect for the time being and although I should have thought of it (I did it for my son'* subaru when we put in two 10" subs) a fuse on the hot side of the battery cable so do the job and with my limited skills I can accomplish that.

26 years September but she'* still my bride. Thanks again be well