Is the TV 1080P?
When you clone the resolution max is limited by the lowest max resolution supported by the cloned displays. You can scale the image to fill the entire screen of the display that supports 1920*1200 but you can not clone 1920*1200 to a display that does not support it unless you use a scrolling mode if supported by your display. Ensure the monitor is the primary display and the GPU should be able to allow a scrolling mode and or down scaling to the TV.
In cloned mode the same image (including resolution) is sent to both displays.
EDIT: The above is really only relevant with a switch box clone, or in the absence of a GPU that can up/down scale an image. My mistake.