Automatic transmission Reverse transmission weakens Audi A8

Hello, everybody!
Please don't kill him first! Have already read a thread here about the death of automatic transmissions regarding reverse gear! With me, it's a little different and wanted to know if you can fix it with an oil change or better an oil scrubbing?
So I have an Audi A8 4.2l 228KW/310PS FL model.
The following automatic transmissions are installed: ZF 5HP-24 ECZ.
==References== 294000TKM. The transmission switches really butter soft reacts immediately to Kick Down and can be easily switched up and down on the steering wheel F1 circuit as well as TipTronic! Only the reverse is weakening! Especially when the Audi is cold, when I take the reverse gear it drives back but slowly and when I hit the steering wheel it almost stops? If I give gas, it's not much more than the rev indicator goes up! When the Audi is warm it is much better there it has more power! But even there it is not as it should actually be, i.e. I press on the accelerator pedal he drives back faster but the rev indicator is then also high! What exactly can that be? Could you tell me what transmission oil is coming in?

I'll thank you in advance for your help!
Greetings Cem