Vibration

Ok has anyone had a problem with their Rack and Pinion unit. Mine has started a vibration after 40 mph and dies after 60 mph. It's not the Wheel balance. However, I just installed two reman. front axles. It seems as though I notice some slack in the steering system. The steerig also rattles over bumps. Just trying to get some input from you guys before I go out and jack it up. I figured that this is another problem that is SVX specific.