Ok, so have you measured to see that when the new bushings were installed, that the body was centered over the frame??
Is that 1.5" as measured from the frame to axle, or from the axle to the body, or from the body to the frame? Big difference in what you have to look for.
Get out the plumb lines, and start making measurements.
Possibilities:
Rear suspension bushings toast.[High miler??]
Suspension mounts pulled out of the frame.
Body not on the frame strait.
Car has been wrecked, and the frame is tweaked.
A 4 wheel alignment, should give you some good info, to start with.