What speed are you running the rotor and what do you have the concaves set at. Which rotor do you have AFX or Specialty’s or standard. Makes a big difference. Rotor speed should be up between 650 and 700 concave between 3 to 5. How many hours are on your rotor bars. 
  Years ago I had a dealer brought me a 1660 with standard rotor and it was the same as yours go 10 feet a had to un plug it.  Clean it out and you could put the slug in a 5 gallon bucket. Couple hours of that and sent it back to dealership. 
 If you are breaking the belt you have a feeding problem.