tranny shift fix
You mention doing a number of adjustments and checks but nothing about service (new fluid and filter) which I have seen/felt cure shift flair. It is characteristic for Mercedes transmissions to have firm 1-2 shifts, alot of people adjust the modulator to try and get an American shift feel which does more harm than good for the tranny by causing excessive slip and premature wear. Assuming your tranny is not ineed of a rebuild I would do an r&r of the fluid and filter looking for excessive debris, also drain the torque converter put it back together if all looks well, next I would have the modulator pressure adjusted back to factory spec, you could do it yourself if you have the correct tools and then test how it shifts. A shift kit for less than $50.00 with those claims might be to good to be true, you would think Mercedes would have done that from the factory.