The pelvis has two ways in which it can adjust up and down, side to side - that is through the SI joint which allows for a figure 8 adjustment, and through the pubic bones, which allows for adjustment. The ankle and knee have another certain degree of variance in which they can adjust.
So if you have two hips that are not level it can be pelvic and back muscles,it can be quadratus lumborum, it can be obliques and rib muscles, it could be knee, it could be foot and ankle....
You may have a tightened psoas, but that does not mean the psoas is the culprit - the illiopsoas usually tries to adjust for differences in hip motion.
I think you don't need this chiropractor. Have you checked the egoscue site? I don't know how an ART release practioner is going to figure out what is causing the discrepency, most 98% sure would probably were not born with two legs different in length - unless you suffered some major injury to the femur or tibia.