I can't imagine the tires breaking loose in 6th gear though.
If you have the ability to log, you can determine if you have DSG slip or your tires are just breaking loose.
What should I log?
I don't think you have a tranmission problem, my money is on a boost issue.
The transmission holds the power just fine. It holds well above this. However the engine ECU will report a calculated torque value to the transmission ECU. When that value exceeds 350nm the transmission ECU will momentarily disengage the clutch packs to lower torque and re-engage them. This is intentional. A DSG flash addresses this.
However on the stock turbo you have a very brief moment where this can happen early in the rev range and we setup our tunes with this in mind to maximize power while sitting just under this limit.
Are you tuned? Before the latest APR update mine did that, it was actually one of the fix