You replaced the shocks and sound absorbing material on your 2011 Sierra?[/QUOTE] I did. I replaced the shocks with the King Coilovers in the front to level it out. I will be replacing the rear either with King's or Beilstein's. As for the sound proofing it is a truck not a Cadillac. I knew that when I bought my TRUCK. So I (with the help of other members on this forum) wanted to make it how I wanted it added sound proofing to the cab. I get tired of people expecting a pick up truck to be quiet as a car.