Using a knife, score ham across the skin about 1/2-inch deep and 2 inches apart. Then, score diagonally forming a diamond pattern. Place ham, scored-side down, in slow cooker. Pour soda over ham. Cook, covered, on LOW 4 to 5 hours or until heated through. Transfer ham to a platter; let stand 15 minutes.
Meanwhile, for the glaze, in a small saucepan combine syrup, brown sugar and mustard. Whisk over medium heat 5 to 8 minutes or until glaze is smooth and thickened. Remove from heat and let cool 8 to 10 minutes. Brush evenly over ham, let stand 5 minutes. Slice and serve.