Looks like there are many LCD panels/TVs out there with a native resolution of 1366x768. That is indeed a very close approximation to the expected 16:9 rectangle, except XOrg keeps showing you a resolution of 1360x768 (or 1368x768) instead of the native 1366x768. Why? Because 1366 is not divisible by 8 and that's not valid in an EDID block. Learn more on wikipedia.
You need a custom modeline in your xorg.conf file …