billnikon wrote:
Try limiting your focus range, I believe you can set your zoom to a more narrow choice, I believe there is a two way switch on your lens, one if for full, and the other is a limiter, try using the limiter, it should help improve your focusing speed.
I have a Canon 7D with a 15-55 Canon lens, it went crazy on focus during a Christening. Had to use manual focus to finish the day. After ruling out the camera body, I found Canon repair center in NJ with a 4 day turn a round. Upon return, the lens has never been better, all my previous focusing issues were resolved. They have a fixed price for the overhaul, a nice service.