Loss of performance over 2.5/3 K RPM

Loss of performance over 2.5/3 K RPM

power curve appeares to be ''n'' shaped , 3k top

Car was mapped S1 at the start of the year
Issues with boost , flutter at high rpm
one power drop during map .....suspected turbo as 180k

New oem recric valve fitted last year , new n75 about 2/3 year old [20 k miles]
Post map , fitted AE stage 1 recon turbo [enhanced bearings , seals std control ]

Ran fine for a while Now appear to have performance to about 3k rpm then ,
open the throttle very little happens

Worst case re-con turbo failed ?..only few 1000 miles old appears to be ok upto 3k
I see pointers to N75 and associated pipes < most likely ?

Tnx-Graham

Can someone confirm bam has qty 2 electrical control valves ?

n75 and n 249 two the same item / part number ? electrically operated solenoid valves ?

Fault cleared Air flow sensor , started breaking up , old age may be , dated 2002 original
item .. New one fitter , something odd with the electronics coating melting ..[perishing ?] normal service resumed

waiting for the next bit to drop off

spoke too soon, power delivery is now, akin to a mad horse .. the new MAF is
working too well .. what now appears to be far too much boost ...
Time for one of those telephone conversations ..