If you've done your fair share of travelling Pakistan's north, the drive down south is an equally enriching experience. Kirthar, Hyderabad just for the pulao, lots to do in Karachi, hub damn, the braces and then Charna island.
As bad as Sukkur Hyderabad is, if you detour off Qazi Ahmed, you can take the National Highway 55 which is a BEAUTIFUL drive, and Qazi Ahmed itself is a very cute town.