1993 GMC Suburban Owner's Manual - Page 86

K231 If youhaveamanualtransmission,youhavea SHIFT light.Thislightwill show you when to shift to the next higher gear for best fuel economy. Whenthislightcomeson,youcanshift to thenexthighergear if weather, road and traffic conditions let you. For the best fuel economy, accelerate slowly andshiftwhenthelightcomeson. Whileyouaccelerate,itisnormalforthelight to go onand off if youquickly SHIFT lightwhenyou changetheposition oftheaccelerator.Ignorethe downshift. Four-wheelDrive Vehicles Only: If yourvehiclehasfour-wheeldriveandis equippedwithamanualtransmission,disregardtheshiftlightwhenthe transfercase is in 4 LOW. ocking If youhavethisfeature,yourrearaxlecangiveyouadditionaltractionon snow, mudice,sandorgravel. It workslikeastandardaxlemostofthe time,butwhenoneoftherearwheelshasnotraction and theotherone does, the locking feature will allow the wheel with traction to movethe vehicle. 2-22