Im not sure about the new DX3 bunk house I have a 2007 350 Grandsport with the M-2 heavy duty chassis . My Dynamax is the last year they put the Cat C-7 motor(350hp) in and its been great . My wife has a hard time keeping it under 70 runs it like her Jetta diesel. I don't let her drive it much .
If I was going to order a new one go Heavy duty everything and get the most hp they offer. I think most of the new ones come with a cummins and check with someone local to see if they are having any issues with that motor. I heard Cat got away from motorhomes because they didn't want to put all the government emission******on their motors. Anyway we love our Dynamax and would buy another one .