This all started with the ported supercharger? The squeal is to much vacuum to the crankcase, your actually sucking the seal into the crank to hard. If your PCV has an oring, then the problem is on the other side. You may have plugged the front port so your not letting air in. Valve cover breather or just removing the oil cap will fet rid of the squeal.
Bad gas mileage could be your boost bypass valve being closed all the time. Are you sure you have all the vacuum line hooked up correct and the bypass valve is open at idle?.
