Boost pressure drop

[BOBO ZENKI]

ok, my boost is dropping to 5psi for some reason. When the car is cold it seems to be fine and boost up to 10psi. Then after punching it for like 10min it drops to 8psi and then 5psi.

I checked all the hoses and lines and they are fine. no other wierd noises or probs.

Any ideas?

thanks