Can you post more details about how you were focusing and the general shooting conditions?
To test the image do this.
1)Ensure your zoom is at 24mm
2)Ensure you are shooting raw at the lowest ISO (50 or 100) and at f/4
3)Take a picture of a text - maybe magazine etc on a tripod with IS on the lens off & with a timer on to prevent shake
4)Do not use flash and ensure you are in a very well lit place - do not have the sun or direct light hitting the picture.
5)View the raw image at 100% in photoshop or lightroom
Look at the image on the computer screen. Ensure you have a high quality screen - newer computers with HDMI will work.
If the text is blurry then you have an issue.
I have had the 60D & 7D and both cameras had a sharp image but not the 5D MK3.