Toba to Shorkot is not operational yet...
you can select M4 portion from Multan to Khanewal then came through Kabirwala, Shorkot, Jhang and then touch M4 again from Gojra. Road from Khanewal till Gojra is 6/10, Single track with pot holes..
Then from Gojra you can drive over M4/M2 till Islamabad.