Transmission/Automatic Problem

All driving stages are illuminated (not yet joined to replace the known faulty electronic part (voltage converter/controller). He has been doing this for a long time without any noticeable problems.
I just can't accelerate faster (max. 2000U/min.), after that it already comes to speed, but as soon as I give a little more force on the gearbox, He rattles and doesn't come forward. Similar to a hand shift, the gear is inserted, but it does not move forward. And this only since it really got cold. A year ago I had the same problem, but everyone had no question marks, after that he stood and this spring I got in and started and started as if nothing had happened!
I haven't found any reliable contacts yet to read out and if I go to an official, then the one that's already at the stop when the bonnet is opened...