Your eyepieces are not likely to be the issue.
Have you checked that the focuser is square? When you collimate to knife edge perfection do you rack the focuser in and out to see if there is any miss-alignment? I am just asking as the blurriness could be that the cone of light might be at an angle to the eyepiece and when focused on axis, the focal plane is at an angle. Are the objects entering the field of view also blurry? <--probably the first question I should have asked!
