I rebuilt my 1999 V6 Mustang, when I obtained the car she was in bad shape. The head gasket eventually blew so I ended up pulling out the engine and rebuilding it. After putting it back together, it sounds great and it's a smooth ride, but there's this tremble. It only happens when I come to a complete stop and my foot is on the brake. The tremble happens every min or so for 2-3 seconds. So did I do something wrong? or have I overlooked something?