Worn bushes in the control arms on the rear axle can give this feeling, and not where you might first look. Ask someone who replaced their steering rack bushes first! Other common wear point worth checking is the lower half of the steering column, there are 2 UJs on it that will get sloppy. Could be bushes on the front lower wishbones too (and might as well check top front arm bushes too). Quite a few things really, but you should be able to check them all by levering with a big screwdriver.