no answer but just some things to consider.

Five speed automatics, I've heard, have a tendency to slam into first or low gear.

A failing AMM air mass meter can cause trans shifting issues, and many AMM's tend to fail at 60K.

Usually flaring is what is described as an upshifting slip? but you mention downshifting. You also mention the problem is new. On my 722.6 C230 it has always occasionally gone into low hard - and at 83K miles it seems fine.

These electronic transmissions can be connected to a dedicated diagnostic tool to find fault codes and problems.