if you want 2nd gear at 80 mph and slamm the shiffter to 2nd it simply wont go. ecu compensates. no lurches. if your close to the rpm range there may be some confusion on the part of the tcu.
go to mbworld.org and search the c32/c55 section for threads by hooleyboy. he drags his s/c c55 constantly and fried his tranny. his has many threads on symptoms and his recent complete renntech heavy duty rebuild for 2500$. afaik he has trashed his more than anyone! diff car same trans as yours