We've been selling these since the 03 model year. Long before Ford and International even thought about throwing a box on theirs.
There is guy in my neck of the woods who did the old Diamond REO deal. Took a 40's vintage class 8 truck and put a late model GM dually box with and updated chassis. A real neat looking truck. I dont recall what type of diesel is powering it.
I haven't heard of any problems. I sell to a lot of the fleets in the area and they are like any other medium duty truck. The GM's have been on the market going on 4 years now so pretty much any problems have been fixed. The only problems I ever hear about are owner inflected. Drilling through fuel and brake lines to install bodies and things like that. The Duramax in these trucks are a different version than the ones they use in the 2500HD/3500.