Screen tearing with duplicated outputs

I am trying to clone 2 outputs for my htpc setup, but have a tearing issue on the TV. I have the computer and a dvi-monitor in one room for the kids to use and a hdmi cable through the wall to a TV for home theater use with a Bluetooth mouse and keyboard. Both 1080p outputs from a 750ti with a g2120 (never goes over 20% during playback issue). Drivers updated, etc.

When the screens are cloned the TV tears badly with no issue on the monitor.
When I remove either output, there is no tearing.
If I put the monitor on the motherboard on-board graphics output there is no tearing.

I would like to clone them so I have the full desktop on both, but by using the on-board display for one of them only lets me extend the desktop and drops a lot of horsepower for playing games. It's a rather old TV and I'm guessing it's an issue with the frame-rate between the displays?

Ideas?

The only thing I can think, is that the refresh rate of the 2 displays are different? So, while cloned, the lower frame rate display has tearing. Personally, I would set up the 2 displays in an Extended Desktop fashion, so that they are running independently, then use the built-in windows functionality to switch between them. You can do it by pressing Windows + P, and you should have the options of 'PC Screen Only', then 'Second Screen Only'. Just change it based on what room you'll be using the machine in.

Thanks, I'll try it out. The monitor is 75hz, but when duped with the TV they are both locked to 60 which is supported by both. I know the TV is pretty old, however, there is no issue with netflix playback off the PS3.

The kids wanted to watch a movie so I detached the DVI monitor and left just the HDMI output in the living-room which leaves no tearing. There is something else or additional issues going on here because it loses audio-sync after 30-45 minutes.Again no issiue with the PS3 direct to the TV via HDMI

This has happened in the past off the mobo integrated output. and I blamed it on the on-board intel graphics or mobo audio.

I have since installed the 750ti, and threw in a xonar card I had to test offloading the audio. Same result. I've updated the mobo bios, contacted evga for output advice, etc. This was at the time positioned next to the TV via HDMI which should rule out a bad cable/interference.

I'm running out of ideas, I guess the only common denominators are the mobo and TV. I suppose I should run a movie off the monitor to see if the audio sync issue happens there after an hour+, but do I run the speakers off the mobo or the sound-card for the test?

I like the solution you listed above, but I also want the kids to know (fear) I can see what they're doing just by turning on the TV in another room...

Inside of that display switching menu, there is also the option of 'Mirror' which would duplicate the displays again but likely cause the unwanted effect. 

So if you right click on the desktop > screen resolution > then right click on both displays > then properties. Make sure that under the 'Monitor' tab that they are both on 60 Hertz.