WARNING: This page is about a different car, the 1995 Oldsmobile Ninety-Eight and 1995 Buick Park Avenue. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Code P1568 Schematic (3.8L) Cruise System Problem (SPS Indicated High)
Fig 2: Code P1568 Diagnostic Flow Chart (3.8L) Cruise System Problem (SPS Indicated High)