Here's a cheap one that someone did. Just need to hook it up to switched power. http://m.imgur.com/a/t2N3c
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From what the manual says about how it works I don't know how easy that would be. Apparently it indicates on the radio screen when it's active.
I also just leased a loaded LTZ and without knowing about the mid year tech addons I feel like an idiot I am usually on top of things like that. Anyway the salesman looked into it for me and as of today it is not available for order yet. I am just glad I didn't get a Denali they are getting the tech add ons plus an 8 speed.
Tahoe 2015i are not available yet or for order? At the GMC dealerships they have the 2015i denalis in stock. I was ready to order a fully loaded LTZ but ordered the Denali 2015i since it was only a 2k price difference.
Anything ordered now would be a 2015i.