Can you provide a sample image at a couple of f/stops. Just from the scenario you give the best I can recommend is to take the lens to a qualified repair center and see what happens.
It would be useful to know what bodies you tried this on, how you determined focus, and what was the focus target. You might also try just the traditional "brick wall" test from a tripod just to eliminate questions about using a three dimensional surface. It's not very useful to know that hair/skin are soft if we can't visualize where these objects are in relation to the desired focus point and the f/stop used.
Roger It's still, ISO, aperture and shutter-speed, right?