I had a problem like that on mine.
It was due to a warped wastefate penny.
£65 later and i had a nice new one from CR turbos and its an easy job to swap but you need a couple of spot welds, i think cr will do it for just over £100

I will post my graph later but id check the penny before spending money on anything else.

Its easy to do, drop the downpipe off, disconnect the actuator bar, put some white touch up paint around the sealing part of the wastegate penny (a band the size of the paintstick is fine)
Then close the penny and hook the actuator back up while the paints wet.
Disconnect the actuator and have aook at how much paint on the wastgate/penny. If not 2 complete circles then u need a new one.
Mine was touching about 20%
after fitting a new one it was like a new car.
Felt like instant boost and twice as much power.


A mate of mine recently had a bog std escos on the rollers with t34.63 and a msd chip off the shelf with seimens injectors, made 375bhp cant remember the torque.