Pentax 55mm F 1.4 Lens

I have been trying a Pentax 55mm F1.4 AW lens.  It is a fine lens except for the fact that it is slow focusing in auto mode and the aperture of choice seems to be F2 in MTF program mode.  As I use it more and more, I am finding that it works best in aperture mode along with manual focusing when used on the original K-3 camera.