Hello I'm new to the site and I have a craftsman zts 6000 26 hrs 52" deck zero turn when I engage the pto in the driveway or in low grass the blades spin freely and strong but when I start moewing and get into taller or thicker grass the blades slow down almost to a stop and you smell the belt burning. I've put on a new belt being that the other one stretched out. any suggestions?