INSPECTION PROCEDURE 16: Transaxle won't Downshift under Load with Auto-cruise Engaged.: Comment
WARNING: This page is about a different car, the 2005 Dodge Stratus and 2005 Chrysler Sebring. However, it is still accessible from the selected car via links, so may be relevant.
A malfunction may be present on the auto-cruise signal line circuit, auto-cruise control-ECU or the PCM.