Have you tried them with other f-stops?
Perhaps do a number of static test shots. Set up a test pattern a few metres away
and photograph it at different settings (mainly of aperture). Use Auto Focus mode at
first, then try some with Manual Focus. This will test if the AF is out. You can even use an extended object, like a vase of flowers, but don't change the camera-subject distance for comparative shots, so use a tripod.
For a test pattern approach,
this link appears useful.
If you discern some focus discrepancy, post it up with photos in a new thread.