You are right on about the planetary failure from the nut. The large drive nut backs off on the 04-06 models due to improper staking most likely, and it slowly backs right into the planetary. When that happens it is usually best to replace the transmission due to the amount of collateral damage. The last one I repaired for this (due to warranty, they won't just replace them but rather fix each collateral failure), it ended up over $7k in repairs.
The problem is that when it starts contacting, it creates a lot of debris as it chews up the stakes in the planetary set, the washer shims in the gears, etc. This debris goes through the oil pump... and it is shot. It goes through the torque converter... and it is shot. Depending on your luck, you can lose the valve body over this too, if the debris gouges the valve bores. Then of course the planetary carrier itself etc.
The planetary carrier that gets damaged is the portion with the four "planet" gears mounted around the perimeter. For this part there is no "Set code", I have no idea what they are talking about. There are only two planetary carriers that were used, and the second one superseded the first one so you get the same one no matter what.
This is the part that gets destroyed by the drive nut: