1998 GMC Sonoma Owner's Manual - Page 199

2-Tiered Loading By positioning four 2" x 6" wooden planks across the width of the pickup box, you can create an upper load platform. The planks must be inserted in the pickup box depressions. Thelength of the planks must allow for at least a 3/4 inch (2 cm) bearing surface on each end of the plank. When using this upper load platform, be sure the load is securely tied down to prevent it from shifting. The load's center of gravity should be positi0ne.d in a zone over the rear axle. The zone is located in the area between the front of each wheel well and the rear of each wheel well. The center of gravity height must not extend above the top of the pickup box flareboard. Any load that extends beyond the vehide's taillamp area must be properly marked according tolocal laws and regulations. Remember not to exceed the Gross Axle Weight Rating (GAWR) of the rear axle. See "Loading Your Vehicle" in the Index. Payload The payload capacity is shown on the CertificatiodTire label. This is the maximum load capacity that your vehicle can carry. Be sure to include the weight of the occupants as part of your load. If you added any accessories orequipment after your vehicle left the factory, remember to subtract the weight of these things from the payload. Your dealer can help you with this. Add-on Equipment When you carry removable items, you may need to put a limit on how many people you carry inside your vehicle. Be sure to weigh your vehicle before you buy and install the new equipment. NOTICE: Your warranty doesn't cover partsor components thatfail because of overloading.