My suggestion would be to down size on your bait. When I have been catching them, I have noticed they will have very small shad in their mouths/bellies. What I have found is that a #2 Mepps will work really well. Also tie on a teaser jig or two above your slab. You will find that they will hit that smaller bait.
Last weekend I tied on several #2 mepps on a A-rig and was catching them 2 or 3 at a time. The #2 spinners are very light and so you if you throw them by themselves, you will have to put on a split shot weight about 16-18" up the line. The teaser jigs work too above the slab.
The guys over on the Bass forum have a saying "match the hatch." If you put on a smaller sassy shad, or little crappie jig, I am sure that will work too...you have to match the size of what they are eating.
Give it a try and see what happens!