So lump burns hotter than briquettes typically. I would quit using the chimney and load your charcoal basket with unlit fuel. Add your smoke wood on top. If using lump try and pack it as tightly as possible in the basket. Close up the smoker open all your vents. Take a propane torch, light it and stick it in one of the holes of the side vents in the base. Run the torch for 3-5 minutes remove. When you get 15-20 degrees above your target pit temp put the meat on. The temp will drop. As it starts to climb start closing down the lower vents. Leave the lid vent wide open for entire smoke. Try and not over shoot your temp by more than 20 degrees as it's harder to come down than go up.
Weber cube work this way too. Just takes a bit longer.