I've had my car for almost 2 years now, it has always worked well

RS6 C7.5 performance with 36.000miles

I was running a DS1 stage 3x alpha (not continuously) with loba HPFP and SRM ethanol sensor + SP lines, with E65
Car made nice power (said dragy), logs looked good

60-130 around 8.3

I then decided to go 2 steps further :

a proper stage 3 with :
DS1
SRM+4 turbos
SRM throttle bodies spacer
CWA100 pump
SRM fuel lines + ethanol sensor
LOBA HPFP
Forge turbo hoses
SRM TCU tune
ER10S plugs

After I installed all this, I couldn't acheive boost target anymore (2.65 bar) and car felt slow
I thought it was maybe the wastegate actuators so I installed :
TurboSystem wastegates
SRM 4 bar map sensors

car then achieved 2.85bar instead of the 3 requested by the map
I thought I had a leak somewhere but after unmounting several times and using a leak tester, couldn't find any

So, there is an issue that means the SRM turbos can't achieve 3bar
But I don't understand why the car is so slow
60-100 is exactly the same as before (8.3)
0-60 is actually worse

anyone has an idea of what could cause this ?

in case someone wants to see a log : https://drive.google.com/file/d/1eLE...ew?usp=sharing