I dont know too much about powerflex bushings either but logically thinking I wouldn't have thought ANY gaps would be good. The original one's (I think you are talking about the front thrust arm, yes?) have a steel insert through the centre which is fully clamped by the bolt through the middle of it.

If it is the design of the powerflex bushings to be the way you have described ie, with a gap, then it may be that because you have installed a harder (powerflex are apparently harder than OEM, which give a firmer feel (read:feel every bump in the road)) bushing, you have now magnified other minor flaws into major flaws. IF you are talking about the front thrust arms have you looked at the condition of the balljoints? Other than these bushes, are you sure everything else is 100%?