Being a 2013 I'd stick to DEX VI licensed products if warranty compliance is a concern. Not that non-licensed products are inferior, but why get into the risk when there are plenty of properly certified products for decent cost. Even W/M has a licensed DEX VI.
Dex VI has some potential issues with older Allison trannies, but by 2007 those were addressed adequately with seal material updates. Your 2013 should have no issues. Dex VI is a very good product with excellent oxidation resistance and vis retention. I'd use it with no hestiation whatsoever.
If OEM warranty compliance is not of concern to you, there there are other good options that are warranted by the lube maker (Amsoil ATL for one example; Maxlife for another) for that application.
The Allision 1000 series tranny was on the drawing board well more than a decade ago; it was designed with TES-295 and DEX III fluids in mind. While GM owned Allison, and GM introduced DEX VI, they forced Allison into accepting DEX VI as a scheduled fluid. After GM sold off Allison, Allison no longer recognizes DEX VI as an approved schedule fluid. Additionally, after selling Allison, GM also kept the rights to manufacture the 1000 series in their Baltimore plant for the light-duty trucks. Allison also makes the 1000 series for other applications in their Indy plant. And so now, you'll see GM 1000 series trannies with DEX VI from Baltimore and Allison 1000 series from Indy with TES-295.
There is nothing wrong at all with using DEX VI in your tranny. It is a good fluid.