I disconnected the wastegate vacuum line and took it for a drive, the best boost pressure I could get was 6-7 psi... So I guess there is something wrong with the flapper or the actuator. It's too hot right now so I can't work on it for an hour or so but I'm guessing it's easy to remove the wastegate actuator, just two bolts and a cotter pin, right?

Meanwhile, the brakes are squeaking a LOT. I haven't pulled the wheels off yet to check them out but I can feel that they need replacing ASAP, probably a higher priority than anything else.