Even without a code there may be a revised "flash" available for the transmission controller. I had a problem with the slow updating of the outside temp display on the 2005 300C I owned which was a required a reflash of the cluster node computer. While the car was hooked up, they upgraded every module including the one for the transmission. When I got the car back, I really was impressed. before the trnasmission flet like the worst part of the drivetrain. Afterwards it felt like a totally different animal.