My GTP stumbles on hard accell under boost. Runs good all other times. Checked values with a Snap on modis and showed 99 % boost all times. Checked and had battery voltage at boost solenoid, though never had vacuum out of it. Check boot control val. Checked and boost control valve seems to be wide open unless under accell. Have good manifold vacuum at one side of valve, but added vacuum to other side ( with vacuum pump ) would not hold. Took belt off supercharger and runs good, of course loss of power. Do either of these valve or solenoid seem to be common, or am I barking up the wrong tree. appreciate any help. Thanks, Don: