If the PC hangs, I may agree it may be a software problem (assuming the PC hardware is proven stable by other means). If the router hangs, it's an entirely different matter.
Even if after changing uTorrent settings the router does not hang, it's still a router defect. It means this particular unit cannot be stressed. This is no different from stressing testing of PC CPU or GPU using special software.
If the router hangs, the router is faulty. One AC87U unit is faulty doesn't mean all AC87U units must be faulty, and does not logically imply AC87U is 雞.