there are a few parameters to precheck before you can proceed to any repair.

1 - how old is the ATF (what ATF is in there)
2 - level of ATF good?
3 - is the electrics connector dry? (if oily then check for ATF in the TCU case)

If all is ok - then get a deep level scan that can interrogate the TCU on MB - some errors will pop up - note them and then proceed. If you see a failure to shift or speed sensor error then you need to replace the electrics plate in the transmission valve body.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)