Bad water pump?

Installed a new water pump on my 360 and after about 5 minutes of run time, coolant started pouring out of the weep hole. As far as I know this indicates a bad pump, but being that its brand new (not rebuilt), before I return this, is there anything else that may have caused it to fail so fast?

I just got the engine back in after pulling it to swap camshafts, replaced the headgaskets, installed new freeze plugs.