The Dodge 48RE's have been plagued with this issue since they we first introduce back in 1998. I recently experienced the same issue coming back from Vacation in early August. Knowing my truck since it was new, and buying from the original owner, I new the transmission with 70k was on borrowed time.
After having the truck at a highly recommended local Diesel Performance shop, the shop manager / tech, gave me the bad news, Torque Convertor failure. He said if I continued to drive/ tow, it would grenade a perfectly good Core for rebuilding and potentially be paying another $1700 for not having a rebuild able Core.
These high performance diesel transmissions from BTW , Suncoast, and ATS will run you $4-$6K with the convertor and that's with a good core to exchange.
The shop I had my truck at, builds Diesel performance trucks for competitions.He has an in house transmission rebuilding shop, state of the art, with both a Transmission Dyno and Truck Dyno, sterile clean assembly room and unbelievable Transmission machining center. He used all Suncoast internals, billet shafts, multi disc Billet Torque Convertor, and Valve Body. Cost me just under $4,000 and 2.5 weeks without the truck. It tows great, my engine temps dropped 20 degrees and fuel mileage went up by 3 mpg. The best part is I don't loose any speed on the hills, maintains within 2 mph.
All in all I have spent nearly $9k in my truck over the past year, injection pump, lift pump, brakes, tires, TPS, Alternator and Batteries. Its an 02 with 73K miles. I bought it two years ago with 47K miles for $10,500 with nearly $20K in it, I still think its better than $65K for a new one :)