Are you sure that's MB?
When you capitalize the letters I read that as megabytes per second and 38 is truly rocking and far beyond what I'd expect from a 300 megabit 802.11n link. My guess is that you are writing about megabits instead.
Try this. Drop the router's speed to 150 megabits on the WiFi and try other channels. It's counterintuitive to some but I've seen it speed up WiFi link speeds. There are more tips but the discussion is a little light on details.