The new transmission started in model year 2016 units. You can tell easily if it has it by looking at the dash...D421 I believe is 6 spd, but for sure if no 4 it's the older one. Technically hp rating goes down with the new trans, but it's the same engine and those that have driven both say new is much better.
Check out RVDirect for pricing info, very easy to get a quote and it's usually a good one. I found only one place that would beat them (and MHSRV by far) and that was MHS2GO which is motorhomes to go in Grand Rapids MI. Felt like I got a fantastic deal, got treated well even after sale and I live 5 hours away.