No I am not using 5 GHz phones. All other devices work fine on the 5 GHz ssid, SP3 is the only one that fails.
I have no other phones other than my cell phones. I got rid of my landline a year ago. Perhaps a neighbor's 5ghz wireless home phone may be a contributing factor with your wifi dropping. Have you tried to connect your SP3 at a different location that uses 5ghz wifi (I.e. BestBuy, coffee shop, internet café)? It would be interesting to see if you find the same issues on a totally different network.