I'm getting lumps of grass when I mulch at 3". If I cut higher at 3-1/2" to 4" its better but the grass is too long. I have newly sharpened blades and the mower deck is clean and sprayed with silicone. I use "Gator" blades in the Fall for the leaves and this works great for that. In the Spring and Summer I've noticed no difference in the clumping so I switched back to Deere blades--with the same results. The mower deck is level and I mow at slow to moderate speed of about 3mph. Any tips?