Transmission issues
 

Hello I've got an audi S6 C7 2012. I purchased it couple months ago and put a rs6 exhaust and stage 2 tune,car went fine for few days then clutch began to slip in reverse and shudder on take off I was told by mechanic needs oil change,so I changed oil and filters then issue got worse,he said it's the clutches ,bought a clutch installed it same problem then they said the mechatronics,changed them still same issue plus another issue arrised.It takes off in 1st to 2nd fine then starts to slip every other gear and in reverse you need to rev the .... out of it till it builds pressure the reverse kicks in. Can or has someone had this issue or knows what the issue is and is able to help I don't know what to do and now there's a new code just come up after installing the mechatronics P179C main pressure valve electronic malfunction, would anyone know what the issue is
cheers

How long did you have the car before you modded it? Was everything fine during that period? How many miles on the car? Did you tune the TCU also? What if you run stock tune? I mean, it's a 12-13 year old car with XX,XXX miles on it. Do you have the entire service history? Any issues mentioned in there?

It ran absolutely fine before the tune I even got it detuned atm made sure it wasn't the problem and no tcu tune it's got 148k kms