The TV must be operating at 2K
Even lower. 6 Mbps is just enough for 1080p and may drop to 720p when the connection isn't reliable.
I'm skeptical that your issue is caused by bandwidth limiting. Your connection may be simply too slow. As @yage said, run a speed test. You may have signed up for "up to" 6 Mbps DSL service but in reality it can be much lower. DSL data rate degrades with distance from the provider's central office and depends on the condition of the phone lines to your home.