I doubt the overboost protection circuit is causing problems with the onset of boost. The darned system gets so gummed up that a more likely failure mode is that it will react too late. As someone suggested, remove the hose fitting on the manifold and clean it. Then TEMPORARILY run a clean hose from the fitting to the ALDA. See if that improves anything. Then check that the overboost protection solenoid has clean and clear internal passages. TEMPORARILY leave the solenoid electrical connector off (or pull the wire off the sensor on the manifold) and see if there is a difference with and without a signal to the solenoid.

If it's the ALDA, good luck. They're not sold separately. Also a PITA to set properly without the proper bench set-up. Lots of guidance in the archives to get it close enough.

Brian, thanks, I did not know that about the solenoid fittings.

Sixto
95 S420
87 300SDL