I can’t speak to video, but obviously that camera is capable of producing clear sharp images. It’s hard to nail down the issue without seeing images and knowing your setup, but here’s a couple of possibilities:
A bad lens: it’s possible it just won’t lock on tact sharpness. Do your other lenses have this issue?
Microadjustment: A lot of lenses are off focus by just a little bit. But this is really only an issue at large apertures. You can set the microfocus on your camera for each lens. I’m assuming you just sent your camera to Canon, not the lens and camera together?
Camera Technique: are you using slow shutter speeds? Maybe it’s camera shake.
Apertures: Are you using apertures at the extreme ends of the scale? Wide open will have a thin depth of field, so only a small portion of the picture will be sharp. Conversely, if you stop down too much then diffraction will soften the entire image.
Filters: do you have any filters on the lens? Cheap filters can soften images.
Also: are you shooting raw or jpg for stills? What program are you using for post-processing?
