There is a problem with the TC design. A common issue with the TC in the 2002,2003 year range of A6 V8's as well as A8's. The seal leaks and that leads to TC clutch failure and occasionally transmission failure.
Audi has a bulliten sent to service centers on the issue. When the Torque Converter Failure code is found, the fix according to the bulletin is to replace the TC with a supposedly upgraded one.
Level10 will take your Torque Converter and upgrade if for about $300. (remove and install is on you!) or sell you a 'new' TC for about $500. They say the replace the parts at issue with 'better ones'. They also do a 'bullet proof' transmission upgrade ?$5000 or so...
I stumbled on my TC issue when my alternator failed at 102,000 miles, other than that I had a leak from the transmission seal at 70,000 miles or so and had the seal replaced, but no transmission trouble otherwise. The only real issue I have had is with the DRC. My car was on of the first two to have the DRC fail and after a 3 month ordeal it was put back to about 90% 'normal' and after the DRC recall "new" design last August it was about 91% of 'normal', thus NEVER NORMAL!
My car is in the shop waiting to hear from the Warranty company! they MAY be paying for a new TC. I paide $4500 for my extended warranty and so far I got $1000 back on the alternator, $200 on a cruise control control stock, $300 on a cooler sensor, so the $3500 for a TC will put me ahead a few hundred LOL...
Mike