I also found with the JD kit that if you set the deck high it could leave a line. I don't think the blades get a good enough vacuum going when the deck is set 3.5" and higher with the JD mulch kit on certain types of stiff blade grass. I mow mine close and didn't have any problems except for the fact I wasn't very happy with the "mulching" ability. Left some pretty large pieces dusting the top of my lawn. I'll be trying the Gator blades using the side discharge on the new machine when it arrives.