you say you clamp off the actuator pipe?? have you floored it at high revs when clamped?? did it still hold boost?do you have a boost gauge?? what boost did it hit when clamped off just curious
id say faulty n75 valve then
the f valve, i had all of them c,f,h,j,k and the f gave the best results
ive got a boost leak at the moment but i used to hit 22psi then drop off to 18psi then hold, it is a stage 1 remap youve got? if so then i dont think you should be hitting 21psi maybe turbo problems?