My '00 Dakota R/T has almost 175,000 on it on the original drivetrain. (Even U-joints too) Only trouble I ever had with the trans was the little clip that holds the boost valve in broke and it started throwing a code. (140,000 miles) I took it to a local dealer and was told that "it needs a complete overhaul". I pulled the VB myself, took the VB out of a trans I bought off the Internet, and swapped them. Trans has worked fine ever since. I have raced the truck, hauled more crap than you can imagine, and pulled my race car trailer with it.

I still get people telling me I better not pull the trailer in OD or it will kill the trans.

I change fluid/filter every 30,000.