2004 GMC Sierra 1500 Pickup Owner's Manual - Page 384

Fifth wheel or gooseneck kingpin weight should be 15 to 25 percent of the trailer weight up to the maximum amount specified in the trailering chart for your vehicle. See "Weight of theTrailer", and "Fifth-Wheel and Gooseneck Trailering" in this section. Do not exceed the maximum allowable tongue weight for your vehicle. Choose the shortest hitch extension that will position the hitch ball closest to the vehicle. This will help reduce the effect of trailer tongue weight on the rear axle. After you have loaded the trailer, weigh the trailer and then the tongue separately, to see if the weights are proper. If they are not, you may be able to get them right by moving some items around in the trailer. Total Weight on Your Vehicle's Tires Be sure your vehicle's tires are inflated to the upper limit for cold tires. You'll find these numbers on the Certification label at the rear edge of the driver's door or see Loading Your Vehicle for more information. Then be sure you don't go over the GVW limit for your vehicle, or the GAWR, including the weight of the trailer tongue. If you use a weight distributing hitch, make sure you don't go over the rear axle limit before you apply the weight distribution spring bars. Hitches It's important to have the correct hitch equipment. Crosswinds, large trucks going by and rough roads are a few reasons why you'll need the right hitch. 4-88