Ya, I agree with MM. The stock 4 link is a crappy design... it actually binds to try and keep it laterally located. When you go to the urethane bushings, you add even more bind, plus you'll have a panhard that needs some lateral movement in order to swing through it's arc.
With the complete global west setup, they actually tell you to drill holes in the RUCA bushings to make them even softer.
You could just get lowers, and keep the uppers... or you could ditch the stock uppers, and get some parallel uppers (steeda or
www.ipschassis.com ) or a torque arm... then your rear roll centre would be dictated by the panhard alone... (lower like the front). This may require stiffer rear springs...