Problem with 1431 New Holland discbine

Have a 1431 discbine, with rubber rolls, that i put a brand new cutterhead on in the spring of 2014. During 4th cutting in 2015 I started to break the drive belts. Turtles appear to all be in time. Checked all fluids in each gear box and checked each gear on the cutterhead. All oil levels were the same as when i checked them before 2015 hay season. Could I be dealing with a bad slip clutch? Any advice would be greatly appreciated. Thank you, J.

Problem with 1431 New Holland discbine