Hi guys

Vehicle in with complaint of black smoke and very sluggish below 2500rpm, then takes off like a rocket.

-We have manually checked operation of VNT actuator with MityVAC, moves clean and free.
-Checked actual position of VNT (block 43) reported in VCDS whilst MityVAC'd and showing 10%-90% or so.
-Checked and cycled EGR via VCDS and saw approx 80mg/s difference on MAF
-Cycled N75 and monitored movement of VNT rod, showed full travel on/off as VCDS cycled test, change of 50mg/str at 1400RPM, so no obvious issues with N75 control or vacuum circuit but VCDS states this needs to be at least 80mg/str ( and normally see upto 150mg/str without noticable issues )
-smoke tested with no noticable leaks.

During road test the vehicle smokes heavily and is very sluggish below 2500rpm, then literally takes off like a rocket.

I have quickly made a chart showing the problem since it is easier to read. Please note this vehicle is remapped, so values will differ from a stock engine. Take a look at the charge pressure control duty cycle against the actual position, and corresponding specified vs actual boost pressure.

During some searching, alot of people are mentioning altering the dead stop of the VNT actuator arm, apparntly its a common complaint which causes the vanes to 'shut' resulting in high back pressure until higher RPM when the backpressure overcomes the vanes and forces them open.
I havent had to do this before so hoping there is something else i can check first, or someone on here can verify this change?