I am having a similar experience with our '01 C320. SAME UPSHIFT EXPERIENCE. The dealership in Austin found no faults, added fluid to maximum level. I suspected controller fault at first, but now think there is a design fault that prevents fluid porting sufficiently when the vehicle is in a turn. Happens with me, but not my wife, so we suspected weight difference, but it happens if she is in the right seat or not.

I will not buy another Mercedes unless the fix this!

(PS: I'm Randy, Mack's buddy, using his screename.)