Network dies abruptly when downloading a large file over wired connection

My Nighthawk is a few years old now and it's probably the best router I've owned to date. Let me preface this post by saying I've used this thing a lot and I've never had a single issue. However, lately when I try to download a sizeable file it kills every other application on my network until I either complete or pause the download. It even kills my other applications on the PC it's downloading on. And by kill, I mean absolutely no network/internet connection whatsoever. I have disabled my Dynamic QoS to see if it would stop feeding all the bandwidth to my download, but no dice. I play a lot of PC games, and thus do a lot of downloading but my wife works online from home. I'm hoping to find a solution that will allow me to download my large files while I'm away at work for the day and not ruin her workday in the process. I have only recently had this issue as, like I said before, I have had this router for several years. Any input at all is appreciated, it's driving me mad.