Log into the router and manually change the SSID (Wi Fi) name of the 5ghz channel.
I often find it is better to keep the 2 broadcast channels separate. For example, I have changed mine, and call one Home2Ghz and the other Home5Ghz.
Some devices can drop the connection when the SSID's remain the same.
Also, you can try manually setting the wifi channel for each broadcast channel. Try channel 6 for the 2ghz channel and 44 for the 5ghz channel.
There are apps you can download that can show the wireless channels in use. For example I use WiFi analyser for Android to show the wifi channels in use around me and this allows me to set the least congested channel.
Give this a try and see if the connection improves.