Sounds like it's just not set up.

I'm assumin your measurements are in bar in which case it's peaking at 0.75 (11psi) and dropping to 0.5 (7.25psi) which would sound about correct, maybe a slightly soggy actuator. I wouldn't DIY this at all and get a tuner to set it all up as there is more than just boost pressure to worry about with a T3 as it moves a larger volume of air at any given pressure