Best thing you can do is focus manually, using the little green dot in the bottom left hand corner of the viewfinder for assistance.
The 'lag' is due to the camera deciding the focus point, passing it to the motor in the lens, by which time the subject hs moved and so it tries to fix again by moving through the range.

Its annoying, but focusing manually, although not a solution per se, is the only option.
Sorry mate.