AC1900 C7000 slow wifi speeds but good wired speed

We have a Netgear Nighthawk AC1900 C7000 Cable modem and router combo. I've been on the phone with Comcast(xfinity) with no luck, and of course Netgear will not speak to me because it's 5 months old!

 The problem; I pay for 200 mbps service, and wired in I get 239.9 mbps but wireless on a laptop capable of very fast speeds, and sitting 2 feet from the unit I can only get at the fastest 126.5mbps on the 5GHz band and the slowest I've gotten is 13mbps! Now on the 2.4 GHz band I get 17.5mbps at the fastest and 1.5mbps at the slowest. I've been logging speeds over the course of a month and those are the fastest and the slowest, most are in the middle. I've read where the latest firmware is to blame, but with the modem router combo I wouldn't know how to test that theory. Can someone please help me get my speeds up?