How do you have the wireless configured on the router? Is Smart Connect enabled?
Disable Smart Connect and go it and configure the 5Ghz radio for single mode N, Manual channel 48, NO WPA security, use OPEN temporarily, Auto channel width. Have the TV attempt to connect to the 5Ghz radio with this configuration. Does the TV connect then and remain connected?
After testing, configure the 5Ghz radio for WPA2 and AES only and test again with the TV connected to the 5Ghz radio, does it connect and remain connected?