2003 GMC Sierra 1500 Pickup Owner's Manual - Page 380

Fuel If your vehicle has a diesel engine, see "Diesel Fuel Requirements and Fuel System" in the Diesel Engine Supplement. For vehicles with gasoline engines, please read this. Gasoline Specifications It is recommended that gasoline meet specifications which were developed by the American Automobile Manufacturers Association and endorsed by the Canadian Vehicle Manufacturers Association for better vehicle performance and engine protection. Gasoline meeting these specifications could provide improved driveability and emission control system performance compared to other gasoline. Gasoline Octane Use regular unleaded gasoline with a posted octane of 87 or higher.If the octane is less than 87, you may get a heavy knocking noise when you drive. If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. Otherwise, you might damage your engine. A little pinging noise when you accelerate or drive uphill is considered normal. This does not indicate a problem exists or that ahigher-octanefuel is necessary. If you are using 87 octane or higher-octanefuel and hear heavy knocking,your engine needsservice. I In Canada, look for the "Auto Makers' Choice" label on the pump. Canada Only 5-5