The 2008+ MY 4T45E tranny is different from all other MY 4T45e tranny's. It was updated for 2008 in order to live behind the HHR SS. For starters there was a different shift strategy downloaded to the TCM to incorporate the hardware changes. The main thing GM updated was the clutches. GM went to "high energy" clutches which are impregnated with carbon fiber. They are designed to withstand heat and slippage better, which warranted their use behind the HHR SS Turbo. There were a few other minor hardware updates to the 4T45e as well.
All 4t45E tranny's that we're originally bolted to a 2008+MY vehicle will have these upgrades from the factory.