Why does connecting a laptop to a TV via HDMI cause a framerate drop?
Solution 1:
The most common problem is that your TV needs to be in 'Game Mode' to enable the proper refresh rate. TVs by default add a lot of processing of the image being presented. You don't notice it when watching TV, but it can cause 'input lag' when playing games.
Without knowing the model, this link should help you in the right direction: How to enable Game Mode on your HDTV.