If it isn't linear blur but rather a general blur, you may just be seeing a very shallow DOF and need to do the AFMA. Shoot some distant lights so the light is essentially a dot. Zoom in 100%, if it is a streak (linear pattern), then it is handle held/shutter speed issues. If it is still generally blurry with not real pattern, I'd lean toward AFMA issues.

Could also shoot from a tripod with 2 sec delay. If the blur issues go away, it is the hand held/shutter speed issue. If you still have issues it is either the AFMA or you have a problem with the lens.