That's 23 hours journey and road condition is also bad.
Following is 15 hour route and most of it is through Motorway
Peshawar to Islamabad (via M2)
Islamabad to Pindi Bhattian (via M2)
Pindi Bhattian to Kabir Wala (via M4)
Kabir Wala to Khairpur (via N5 National Highway)
Khairpur to Karachi (via N5 National Highway)