Current only flows through the resistor pack for 1-3, its a direct feed for 4. On some models, but not as common on Focus, the resistor pack connector gets high resistance on the contacts and burns them. If the feed contact is burnt, no reduced speeds.
The dealers have been known to offer to supply the 'repair kit' with the replacement resistor pack.

So inspect and check the plug contacts as you've alreay changed the resistor.