993 Turbo boost problem

[Brucha993]

Help,My 993tt has boost curve problem.
It is using and FVD ecu. Boost peaks 1.1bar at 3750rpm then dives to .6 at 4000 then gains to .8 at 4750 then back to .6 at 5000.After 5500 it climbs back and reaches 1.1 by 6000 and holds. The torque curve is ugly!
There are no fault codes.
We have pressure checked the intake system,all ok.renewed the boost control valve.Re-chipped the ecu,tested the turbo vacuum units and all hoses.
Any ideas ??