A bad vacuum solenoid won't cause overboost issues, only underboost ones. What DTC code are you getting?
But the modulator valve, PN 52109543AA, could cause overboost, but it would be very unusual, it too usually only causes underboost problems.
The most likely culprit is the MAP sensor or sticking turbo vanes. The vanes can be lubricated and exercised manually using some good penetrating oil.
Just be sure and disconnect the vacuum hose to the vane actuator when you manually stroke them.
Try changing the MAP sensor and see if it fixes your problem.
Use the GM MAP sensor GM 55206797, or New GM PN; 55568175. IDParts sales them and also available online from Amazon and several GM parts vendors.
the part number!
Much cheaper than the OEM sensor and it works perfect.
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