With a 2009 Unit, the transmission fluid should have been Transynd when it was new and when it was changed. I assume that the 6 speed Allison specs were used and the spin on filter was changed and the unit was refilled with Transynd. Dex III will work fine although Transynd has a longer lifespan and generally runs a little cooler.
One thing that should be checked is for broken welds where the chassis is attached to the front cap. These sometimes will break and cause the front end to be loose and shake. Not a serious issue and something that can be corrected with a little welding. These weld issues can only be seen by crawling under the coach and looking up in front of the front tires.
You should find that the quality of materials used is on par with many much higher priced DP's and much better than the entry level DP's. The standard cabinets were solid Alder wood with Options for Cherry and Mahogany. You should also have dual pane windows and better insulation than most comparable coaches.
Naturally none of this matters if the previous owner did not do the required maintenance and allowed the coach to deteriorate.