Check all vacuum hoses and connections from brake booster across engine to turbo vacuum modulator valve.
The small plastic vacuum tubes are known for collapsing and / or cracking which causes low vacuum to the turbo vane controls.
This in turn can cause low boost issues as the turbo vanes are not being positioned correctly as being demanded by the ECM.
Some owners like myself have replaced all vacuum tubes/hoses with high quality silicone hose which is impervious to heat and oil exposure. see enclosed picture.
When I did mine, it improved turbo response time!
You should also add a mechanical boost gauge to see exactly what the boost pressure is during acceleration when you are getting the low boost DTCs.
The three known items besides the vacuum & boost hoses that can cause boost control issues are:
MAP sensor,
Vacuum Modulator valve,
Vacuum Solenoid valve. (this valve normally is open or shut, it can also be bypassed, removed from the circuit to test. see diagram)
Silicone Vacuum Hoses:
Vacuum Solenoid Bypassed:
