Automatic despite overhaul in emergency run

Hello.
my dad has an Audi V8 Bj 89 from Abbot.
It's got about a quarter. 300hp (nock wave) and goes according to Tacho almost 300. At least faster than my sister's A8.

He was driven a truck backwards to the car and the car was about . Moved back two meters. the automatic was on P.

The car has been repaired. Sheet metal, etc. The gearbox was in emergency gear. So it was expanded and drove to ZF in Munich and overtaken. Complete, also wear parts.

But our Wekrstatt won't make this thing work.
Time and time again, he is drinking about 20 liters, even on long distances.
The overdrive only switches very late, if at all.
And it's got a lot of slip, and there's always an emergency run, i.e. all lamps light up at the gear indicator.

Before, I bought a transmission computer at ebay, which will be tried out. What else could it be?
The control unit would be installed in other V8. It was normal.

Possible mistakes?

Thank you

Stefan