robert,
Assuming you have the 5 speed 5G-Tronic automatic gearbox, your experience sounds a bit unusual.
On the previous generation cars - C200, C220 and C270 CDI models - the 5G-Tronic gearbox was more than capable of handling the torque from the C270 engine, and indeed the C270 engine was detuned for use with the manual gearbox.
As Roger suggested speak with MB, and have the gearbox oil changed.
Robert