We are all assuming you have STOCK springs at stock height. Is this true? The shocks must provide the CORRECT amount of damping for the spring force, too much or too little can give a poor ride and control. The shocks you buy are built to provide the desired damping for the amount of spring force that comes stock with the vehicle. If you put on different springs or changed/raised them some how, then that could change the damping force needed and new shocks would not work correctly. If the suspension is stock and correct height, then I would suspect wear in the suspension if new shocks are still bouncy. Not only bushings, but ball joints as well, the track bar and tie-rods. You really need to inspect the entire suspension and look for worn out and damaged parts.
Polyurethane usually performs better than stock Rubber Bushings. Well better in control and tightness of the suspension. They are harder than rubber and can be a little stiff and even make noise, like squeeking if they are not lubed. Some brands of Polyurethane have graphite impregnated in them to ward off the squeeking.
Worn or damaged bushings will make the suspension loose and lack control, so the big thing is too replace them, stock bushings will help regain that OEM ride and control, if the old bushings were worn or damaged.
Swaybars don't carry much shock, they just tie the 2 sides of the suspension together to help control the suspension better. People do use OEM Rubber bushings in the rest of the suspension and Polyurethane bushings in just the Swaybars and it does work fine.
When I've used the polyurethane bushings in MacPherson Strut Vehicles, there was NO harshness, just better control and a tighter feel to the suspension. BUT, MacPherson Strut Suspension take all the shock and load in the big strut/shock absorber itself, all the links are just there to hold the strut in place. Jeeps don't have MacPherson Struts, the Front Suspension of my '69 Charger has Poly bushings, its a double wishbone type suspension that carries the load/shock thru the double wishbones, so there was a little extra harshness and an occassional squeek. The Jeep front suspension is upper and lower control arms, a little like double wishbone in a different direction, so I imagine it would responde similiarly to my old Charger.
