Could be anything. Maybe the torque converter bolts.

 

Well she went into the shop... torque converter is toast... and its possible it took the transmission with it. Wont know till they open it up. Crazy expensive...might not get it fixed...if just converter, $900, installed. If its the transmission as well..$1900 for transmission and converter. Little much for a truck thats 18 years old and has 389000+ km on her.
We will see....

 

Or you could look for a good used tranny in a bone yard...probably $500 or less.