Sigma 24-70 mm, f/2.8

I just bought Sigma's 24-70 mm, f/2.8 EX DG lens for my Pentax *ist D. I
intended for it to replace my 28-80, f/3.5-5.6 Pentax lens for basketball.
However, I'm finding the Sigma slow to focus, resulting in a lot of pathetic
shots. My Sigma 70-200 mm, f/2.8 EX focuses well. Does anyone else have the
24-70 Sigma? How fast does it focus?