Tillers

I have a new DRT900H. I am using it to till a new 4000 sq ft garden. The tiller runs very well, but it is chewing through the clevis pins that serve as shear pins on the tines like there's no tomorrow. At times I have tilled for less than a minute and sheared a pin. I estimate that I have broken 60-70 shear pins in digging this garden. I thought that once the garden was established I wouldn't have as much trouble as the soil would be loosened and easy to work. I was wrong. In less than five minutes tonight, with the tines rotating forward, at half throttle, just running it between two rows of plants, I broke the left pin, twice. Has anyone else reported this problem??? This is very expensive and very frustrating to live with!!!