The reason why the car is breaking traction at speed with the tune is due to the additional torque. And I'm assuming you are actually accelerating when you are losing traction. But if say you were going through a constant radius sweeper and constant speed, and the rear loses traction more now compared to before, it is simply down to the fact that your tyres are losing its peak performance. 10k km is a lot of k's for rear tyres with this much torque even if they still look like they have tread on them.
Haha, you will never get the sensation of rear end grip like a 911, ever! No other car feels like the 911 when it comes to rear end stability and grip. This is all down to the weight of the engine in the rear, the fat tyres and superior suspension tuning. I know 911s very well, having owned many in the past. My last two were 997.2 GT3s. Only one way to fix this - buy another 911.
