Simplicity like to put quite the twist in their drive belts, belts other than OEM do NOT last long at all. Espicaly mower deck drive belts and some engine to transmission belts. Check for any noisy idler pulleys, if its not smooth and quiet, replace it. Then check the driver and driven pulleys to see if the edges are worn to the point of being like a knife, be carefull doing this, they can become a razor blade if worn enough! Then get a proper OEM Simplicity belt from the dealership and see how that works. If you need further assistance, PM me for my cell number. Mike