According to the mechanic, the computer that controlled the transmission failed and no longer pressurized it properly. This caused it to burn the fluid and burn out the transmission. The computer is apparently mounted onto the engine where vibration and heat are common.

Disappointed that the transmission would fail at 69,000 miles on such a nice truck! But the transmissions on these Dodge trucks have this reputation of unreliability. The truck is great but, if you buy one, plan on upgrading the transmission to something more substantial and if yours goes out, don't have them rebuild it at the dealer to give you the same thing because it will only go out again.