I think with all the "refinement" GM has done with these trucks they have become very finicky when you do anything outside of stock. The 10 sp Alli is the transmission going forward, and GM would know over the next 5 or 6 model years the power would be going up.....so it must be capable.
There will be those in the aftermarket that will claim the transmission has a weakness and is a time bomb waiting to explode, unless of course you buy their parts to 'fix' it. The older Allison's are amazing transmissions but there were dozens of vendors selling fixes for weaknesses they convinced customers were there.
If you're going to high hp tune, have parts fall off etc, well, then that's on you. The 5,6 and 10 speeds can all fail or need upgrades to handle what you've decide to throw at it.
Since the EPA did what it did, most of the reputable tuners got out of the delete business, and IMO based a lot on what I read on here, the delete tunes now are sketchy as hell and lack the quality of the tunes back in the day from the bigger tuner companies, who did the work to make them safe. As things on the truck get more connected and computer complicated I think the problem only compounds itself as the margin for error is waaay smaller.
Basically, if you're gonna screw with these trucks, don't be shocked when the truck says no way, and parts fail or you send the technology so far out of whack things self destruct. 5 or 6 or 10 speed, GM or Ford or Ram, if you've killed it in 15k that's you.