Yep, it is a tranny issue, so best to re-post over in the AT forum. Include a tranny description.
* Have it scanned with VAGCom (not sure that generic scanners can get codes from the TCM)
* Check the fluid level. There are howtos over in the AT forum FAQs, it's not hard. Basically: just wait until it is a certain temperature (by VAGCom, thermocouple on the pan, or your calibrated hand), then remove a fill plug. Add till it just dribbles out then re-install the plug.
* Check the condition of the TCM; lots of times they are wet. If so, start looking for a replacement (using the exact TCM P/N)
* It didn't happen before because you had no torque to speak of. Now you have a little more, and it will (or can) slip just like a manual if it's on the way out.