I just left Bolivia last month. All the roads in the southern half of the country are dirt. Worse than that most are in the process of being paved and the detour roads can be a real drag - I wouldn't want to take many of the roads during or after rain, which they are now in the rainy season. The road to from Potosi to Sucre is paved, but I don't think you can get to Potosi on pavement - maybe by staying on Hwy 1(?) I went thru Huanuni and that is where the pavement stopped. No way of getting to Uyuni on pavement, and again, the road construction sucks. The road from Uyuni to the Arg. border is amazing and solitary - no construction.
Good luck avoiding La Paz, not a fun drive getting through there.
I do plan on returning to Bolivia in a month or two and will enter through Chile to avoid the southern dirt roads during the rainy season.
Left Seattle March '09 for RTW trip.
'02 BMW 1150 GSA