They are supposed to according to the truck equipment pro's that I ordered them from. I lost 5 to 6 inches when I put on rack, tool boxes and other stuff I carry with me all the time. A friend who has done this kind of work for over 30 years steered me this way when I told him I wanted to bring the rear end up.
Online they were 498.00, I got them for 370.00 from a local truck shop. There are light, medium and heavy duty. I went with the medium or 2500 lb rating.