They must be factory installed for all 4WD trucks. Fits my 2015 Silverado 2500hd easily. Took about 2 hours for the bags and another hour for the wireless compressor. Big difference when towing heavy loads. Being able to rear-align a 15,000-pound truck helps with just about anything. Steering is better, no float. After their installation, the feeling that the white joints were separated disappeared. At 35 psi, the truck feels loaded like it should from the factory. Why call a truck a heavy duty truck and not turn it on is beyond me. Why does GM think we buy these trucks for Sunday trips? Headlights shine where they should. If you use your truck to tow and haul heavy loads, or if you have a long platform and bumper to tow something. Buy them and a cordless compressor. Be the investment you can make in your work truck. I also installed a rear stabilizer bar from Hellwig Big Wig. Together this made the 2500hd a different truck when towed, and air pressure dropped to 5psi with no load. I can't tell any difference in driving behavior. I'll install them on my new Silverado once it gets here.
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