OK, so I think you have found the issue :)
How are you configuring the THS8200? Is it slave or master timing?
Are the H & v outputs from the processor correct?
Are you using discrete syncs or embedded syncs between the processor and the THS8200?
Use the configuration setup files from here to configure the THS8200 correctly for your specific configuration...
http://www.ti.com/product/ths8200
The first and most critical thing to get is the monitor to detect the correct output resolution from the THS8200, then we can work on getting the image displayed correctly from the frame buffer.
BR,
Steve