I'm having an issue with wifi as well. I tether my gs4 to my verizon unlimited hotspot for use at home and the data terribly slow. Subpar 3G speeds when I download apps from the App Store. I've seen something about going into the wifi menu with *#0011# but that does nothing on my verizon gs4. Any help from fellow verizon users?
To answer you, Samsung has acknowledged wifi issues with D-Link routers and their firmware.