Grant switched from being a player, before Vicksburg, to being the manager, after Vicksburg.
After Vicksburg, Grant had an unlimited bank. After Vicksburg, it was as if he was managing three players, Meade's Army, Sherman's Army and the Navy, all playing at the same table with one Confederate who was a good player, and another who had already lost his stake and was pawning his jewelry to stay in the game.
One of Grant's players was likely to win in every hand, and when Sheridan joined the table, Grant never lost another hand.