If you stick with that lens test it for focusing accuracy before photographing something important. Several years ago a friend had me photograph his visiting family with his camera and all the photographs were out of focus even though I carefully composed and focused each frame with the camera on a tripod. He happened to be an ophthalmologist and suggested that I make an appointment to have my eyes checked. They were fine and he happened to remember having dropped the lens but it showed no damage. He sent it back to Nikon and they found a lens element had shifted.

http://www.jeffreyglasser.com/