After doing a head gaskets and rocker rebuild and valve lap my motor has a rough spot at 3000rpms which lasts til about 4300rpms, where it gets better but is still there till about 5000. ironically the motor is smoother and quieter now up until it reaches 3000rpms. They only shaved 0.005 off the heads so i dont think it's a preload issue, what else could it be? Cam? Flexiplate? Balance? Damaged rocker or valve?