[sperry]

Think of it this way:

If you have nothing connected to the wastegate, it stays shut all the time and you overboost.

If you have a simple pressure line from the turbo outlet to the wastegate, the wastegate opens based only the resistance of the spring pressure of the wastegate to the absolute boost made by the turbo, which is around 6-7psi IIRC. This is known as "wastegate boost".

If you T a boost controller solenoid into that simple pressure line, the solenoid can bleed off pressure in the line making the build up of pressure on the wastegate actuator delay opening the wastegate, thus allowing higher levels of boost than the base "wastegate boost" level.

If your boost control solenoid is out, then your car should boost like it's got a simple boost line between the pressure side of the turbo and the wastegate, with a hole in it. Which would result in slightly higher boost than "wastegate boost". Which is exactly what you're seeing. So try trading the boost solenoid and see if it fixes the issue.