Connection Speed drops from 60Mbps to 30Mbps

I'm on a 60Mpbs plan. Whenever I test it, it normally tests right at 60Mbps. Over the last month or so, I've often notice my browsing response time (wireless) getting sluggish and do a speed test. Speed test shows 30Mbps. I plug PC directly into the modem and it tests at 60Mbps. When I turn the router off and back on again, my wireless speed goes right back to 60Mbps

What could be causing this besides a faulty router?? T.I.A.