i know when the motor is cold they apparently have a safty fetaure that they will not reach full boost when cold. (to protect the motor) also same with when the motor is hot, when it reaches a certain temp it will boost no more then 8psi... and it feels like it hits a brick wall when it comes in. This is a saftey boost cut feature.
The boost guage shows 8psi like you say when it happens, so it must be the problem.