You said 15" vacuum after the solenoid. This implies the solenoid is working correctly.
If that doesn't convince you, put a dwell meter on the solenoid wires. You should see about 70%. Read the wastegate duty cycle with a scanner. They should be about the same.
The Constitution needs to be re-read, not re-written!
If you can't handle Dr. Seuss, how will you handle real life?
Current oil burners: MB GLK250 BlueTEC, John Deere X758
New ride: MB GLS450 - most stately
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510