Yeah, I see, you want to take route via Trebinje and Cemerno Pass. Do you know how to reach Trebinje from Dubrovnik? It is not trivial for foreigners, since there are no road signs in Dubrovnik pointing you to Trebinje (this is due to the fact that Trebinjans shelled Dubrovnik during the war, so city is in a sense ‘erased’). You will take a road to Cavtat and then few miles from Dubrovnik and well before Cavtat there is a sign for Brgat Gornji and BiH. Take that road it leads to Trebinje.
Now in this entire trip Trebinje is probably the most interesting town to visit: you have old city core with the old bridge. Excellent winery and restaurant at Vukoje winery, ask for the directions in town. His vranac riserva is subperb.
After Trebinje folov signs for Bileca then Gacko then Foca. You will be crossing Cemerno Pass which used to be the most treacherous point on the road. I deove it few times and if you have done Asia driving, it should not be a problem. However few years ago they did some road widening and improvement so it might be even better now.
Once you cross Cemerno you can stop for a coffee at Tjentiste. It is a site of a huge ww2 battle between germans and Yugoslavs. There is a monument in pretty bad shape. Also once you cross Cemerno observe surroundings: mountains are marvelous and you will be near Mt Maglic, highest peak of bosnia.
After Tjentiste you will descend to Drina valley and pass Foca and Gorazde. After Gorazde you will go through Drina Canyon, very photogenic area. Especially spot where Lim flows into Drina.
After that you will be in Visegrad: but here is a spoiler: besides the bridge, not much more to see.
In all road is very good with the possible exception of Cemerno pass.