I had the exact same problem on my 2001 3.0 earlier this year. Very rough vibrations when transmission in drive at full stop (would go away in neutral and park, or when driving). Changed the engine mounts and 90% of the vibrations went away.

Changing the torque converter resolved the leftover vibrations, but the reason for changing it was because I also had some shaking when accelerating, so getting rid of the rest of the vibrations could be considered a bonus. :P