What kind of OG was it? The warm season grasses (panicums, miscanthus, etc.) do not take well to either late summer /early fall planting or transplanting. Their roots enter into a period of dormancy at this time and they just have difficulty in establishing before cold weather sets in.

I would definitely cut them back hard so they are not focused on foliar growth and can concentrate their energies on the root system. And keep them deeply watered (but infrequently) until fall rains arrive.