The model is a professional series 5 plus. Manual says not to exceed 12 cups of flour, not total batch size. It also noted not to use more than 6 cups of whole wheat flour.
Well, if the cups of flour are around 4.4 ounces each and the final dough is around 165% of total flour, then it is
12*4.4*1.65*28.4 = 2,474 grams total. So, that is roughly the capacity.
Your dough was 1300*1.65 (about) = 2,145. You were close, but under.
As mentioned, Craig goes much higher, I keep mine at 2,000 or less. I think there is a gear in there that is replaceable that is the first thing to go under heavy loads. Mine may be heading that way.
Is yours new? Old? Mine is about 4 years old.