Upvote:1
There are two main different routes between the cities all of which pass through Malawi and Tanzania/Zambia
If you use the more popular Tanzania route passing over long stretches of B6 expect stretches to be Paved/Unpaved and thus bumpiness and traffic is inevitable on portions of your journey. A straight trip will take about 33 hours however with expected breaks from boarding different buses, expect a little under three days.
https://en.wikipedia.org/wiki/Transport_in_Tanzania
Enjoy