Since Ive had my 2 JD z tracs I have experimented with doubles with the mulch kit, tried the gators on top of med. high lifts, high lifts on top, gators on top of flat blades and all other combos with no big difference. Yesterday I done a yard of pecan leaves and had to go over them 2-3 times to mulch them up good. I will say the 717 beats the 737 hands down on mulching but cant say why. I took some old gators I had for my 717 and put them on my 737 with the shorter gator (16") on top of the longer blade (20") and it worked great. I did another yard of pecan leaves, dog wood, grape vine, and pine straw and it got it in one pass. Just wanted to let you folks try it that have the JD and are thinking about mulching, the heck with bagging when I don't have to!