You can't have the guy get limited touches and expect he's going to be explosive on every one. Like most backs, he needs a lot of touches in a game to get into a rhythm and start breaking tackles later in the game. He also needs the ball thrown to him more. This workload management is hurting the team and not really helping Todd much either.
Maybe it's better to have him split carries more by game, than splitting in-game. Meaning let him carry the load for a couple weeks, then let Brown carry the load for a week or 2 to keep Todd fresh.