Communications at mmWave frequencies will be a key enabler for the next generation of cellular networks, due to the multi-Gbps rate that can be achieved. However, before this technology can be widely adopted, there are still several problems that must be solved, primarily associated with the interplay between the variability of mmWave links and the complexity of mobile networks. An end-to-end network simulator represents a great tool to assess the performance of any proposed solution to meet the stringent 5G requirements. Given the criticality of channel propagation characteristics at higher frequencies, it is of fundamental importance to properly simulate detailed propagation behaviors. Towards this goal, in this paper we present our implementation of the 3GPP channel model for the 6-100 GHz band for the ns-3 end-to-end 5G mmWave module, and detail its associated MIMO beamforming architecture.