1. When you are riding a horse and pulling a cart, cart's speed remains low and horse's speed remains high. Looks and feels pretty stupid.
2. When you are riding a horse and pulling a cart and pick something up, cart's speed becomes lowest, but your horse's speed remains high. Looks even more stupid.
3. When terrain type changes while pulling a cart on a horse, cart gets unhooked and stops.
My idea is to make these two match. Either horse's speed or cart's speed.