I assume you are referring to a 5 Ghz Wi-Fi signal or is the modem a 5G Mobile Broadband Modem with Wi-Fi?
Have you verified that the TV has the capability to link to a 5Ghz Wi-Fi SSID? Most legacy models only support 2.4Ghz. If your TV has 5Ghz and 2.4 Ghz capability (802.11ac) and prefers to link to the 2.4Ghz network instead of the 5Ghz network, it is doing so because it provides a stronger and more dependable connection.
Are you able to move the modem closer to the TV or have a LAN cable connection. If not, suggest a pair of Powerline Adapters like the D-Link AV500s.
Hello Peter - the majority of 5Ghz Wi-Fi is generally delivered on Gateways that support the 802.11 ac standard due to its higher speeds and additional functionality. The older 802.11n standard also supports 802.11a 5Ghz but as it is limited to a best case laboratory maximum data rate of 54 Mbps, it never really took off in Australia due to its smaller coverage area, weaker signal and 802.11n overtaking that limit. Its basically an abandoned rarely employed standard and may explain why some people's experiences with modems has been disappointing when they set their devices to 5Ghz - my Apple iPhone 5 is a 2012 model with 802.11 a/b/g/n - its faster and with a stronger signal on the n.
5G LTE Mobile uses 3.5 GHz frequencies. Cheers
I am on the same learning path as you and by means an authority on technological matters. I like to read about technological articles on the web to acquire knowledge on the theories of communications but find they are generally not written by gifted writers, making it a challenge to come to grips with understanding the complexities of it all. Putting whatever knowledge one distills from that research into practice, by trying to solve issues, is an pleasing activity when it circumstances match but as with technology, not always the case. Unexpected or unexplained things occur and then there are equipment faults! I do enjoy reading your posts. Cheers.
I'm glad you two worked out the OP's question, I was scratching my head wondering about 5G and TV.