How do I sous-vide a shoulder of lamb?
I would sear first, both to begin flavor development and to kill any bacteria on the surface of the meat.  Bag with or without herbs and a small amount of liquid.  Cook sous vide for 18 - 36 hours at 165F/74C for well-done/traditional braise texture.  Then before serving, I would have a very hot oven ready.  Carefully remove from bag (it will be very tender), pat dry, and finish in hot oven to finish browning.

At the end of the day, you just may prefer roasted/braised to sous vide.  It's just another tool/technique.