Code 55, ECM/Pcm Error
WARNING: This page does not describe the selected car, but rather 18 other vehicles, including the 1995 GMC Vandura Special, 1995 GMC Vandura, 1995 GMC Suburban, 1995 GMC Rally Camper Special, and 1995 GMC Rally. However, it is still accessible from the selected car via links, so may be relevant.
Ensure control module grounds are good and MEM-CAL is properly latched. If okay, replace control module. Clear codes and confirm closed loop operation. Check operation of SERVICE ENGINE SOON light.