Anyone who may be able to help or has ANY info at all on lowering my 2011 GMC Sierra 2500 HD 4x4 I would really appreciate it. I know what'* going on as you read. Why would you want to lower that truck? The story is that this was left from 2011 and the dealer gave it to me for the same price as the 2012 1500 4x4. That is why I have it. Unfortunately it won't go into underground parking lots and I really need to get in them for work.. Sometimes I regret taking the bigger truck but could not resist at the time. Any help would be appreciated. Thanks.

How over height are you? if just a inch or so lower profile tires may be a possible course of action, but not sure the options available for a 3/4 ton truck tire.

You could lower the front end a couple of inches by turning the torsion bars down. As far as the rear end, you might be able to remove a leaf spring. But you jeopardize its hauling capacity to do this.

stylintruscks has a 4/6in drop available and like mentioned you can use smaller tires to gain more
CA2507-4 RK2507-6 DJM Suspension - Lowering Kits At StylinTrucks.com

mike 2007 up dont have torsion bars any more

Oh, I didn't know they stopped using t-bars after 07. My bad.

Thanks guys. I seem that Djm had something but I asked a local supplier to look into it and he said that he called Djm and that they had a generic one for 1500'* and nothing on 2500 HD'* I am going to contact them directly and find out because they do have the option. If that works then it will be exactly what I need.