Yup the Dodge auto is a piece of work I dont think I have heard anyone yet say ooh get one with an auto at least in a diesel Dodge. I dont know what the truck was used for, how many miles are on it or if it has an Edge EZ or Juice Module but at this point the tranny needs some attention.
I have a 48RE in my Dodge with a Cummins 600 motor I dont have any mods done to it and it goes into gear and shifts great, Ive been told if I leave it alone and change the trans fluid per DCs recommendation the trans should last well into the 100k mile range. I dont believe it but thats what I am told.
If you plan on pulling the Edge stuff off and going back to stock you would probably be ok with a stock trans. If it were my truck and I needed to rebuild the trans I would look in to a Suncoast,DTT,Gorend trans just to name a few and leave the Edge stuff on because you will have the advantage of the added fuel mileage and you will have a strong enough trans to handle the power when your done.