When I bought the truck, the rear end sat pretty high and I like that because it meant I could put a hitch on the back of the truck but not drag it when entering my stupidly-steep driveway approach. However, as I added weight in the back of the truck and as the rear spring pack settled, the rear lost several inches of height. I could have taken it to the dealer and tried to get something done about it but I installed a set of aftermarket shackles instead. They are made by Daystar and install at the rear end of the leaf springs. You can see them here in this pic, they are the clean gold "things" visible above the mud flap.

The install was pretty easy. I had all the right tools except one. I guess I don't have one because I don't know what it is. My only trouble was when I was ready to hook up the new shackles, the truck was sitting too low since the new shackles were 2" longer. I couldn't raise the truck any higher and I wasn't able to pull the springs down far enough to get the shackle holes lines up with the spring eyelet. As you can see in the pic below, I decided to use the OEM jack to push the spring down that 2". It worked like a charm.