I would suggest:
1. Make sure your cooking surface is at least 225 degrees. The grill surface can vary from your temp dail in the door.
2. After about 1.5 hours wraped I would probe in between the ribs with a tooth pick to check for tenderness. The tooth pick should go in like it is going into butter. Don't be afraid to go longer.
The best advice I can give is to just keep cooking - I don't know anyone who just walked up and started putting out consistent Q.