My dad has one. Its purty. He replaces his 2000 Ford superduty V10 with the new Chevy and its alot smoother and more torquey. That Allison tranny is something else. We were coming down Ashton hill with his big fifth wheel and he didn't touch the brakes once. The tranny knows what to do all by itself.
The only problem he ever had was that when he left the dealer lot, he gassed it hard and one rear tire broke loose off the rim, instant flat, instant aluminum wheel spinning into asphalt. Dealer replaced the tire and the rim.
I found that it was way to easy to get the rear end to break loose but that's a first for me. I love the Allison to. Here in AZ we have a few hills up north and it's great for pulling. I think my breaks will last me a life time with that tranny. Thanks for the update and let me know if he runs into anything on it.