Hello.
Did they check the condition and the level of the ATF fluid?
I think that after 11 years, you maybe need a tranny fluid change.
At higher speed the transmission need a lot of oil, and sometime
even a very small leak over the years can cause a low tranny fluid.
It's an easy DIY, and you can use VW/Audi oil G052162A02 or
Pentosin ATF1 since it's cheaper an it's the same as the Porsche one.
The ZF 5hp19 transmission was also installed in the VW Passat and Audi A4.
link to ZF transmission
Link for the DIY of the 5hp19 fluid change
Good luck