If you eliminate other options, check PMI inputs that are high speed precise switching LU , LD , DZ, etc. Keep in mind position count updates/ corrects when passing through leveling vanes. MAKE SURE THEY ARE NOT CRYDOM. If they are Gordos or Grayhill they are probably fine. The CRYDOM PMI modules are slow switching and could cause leveling, position, ntsd, etsd errors.