Running 3 monitors on 3.1 Mac in Yosemite

I am running a Mac Pro 3.1 2 x 3.2ghz Quad Core with 32gb Ram. I have been running 3 x monitors - 2 x 1920x1080 24" monitors and a Sony 32" TV. All had been running fine. I recently updated to Yosemite and all continued to work well until last week I had a catastrophic system drive crash with the drive unrecoverable, and my cloned drive being a little old. I decided to jump right in and re-install my entire system, production software, plugins etc etc. I have done this and the machine actually runs better now except for one thing, the 3 monitors no longer work, only the 2 x 24" monitors. I have two video cards - an AMD Radeon 6870 2GB and a GT120. I have the two 24" monitors connected to the 6870 and the TV connected to the GT120. As already stated, it had been working fine prior to the system crash. When I boot the system, the Apple logo and bar come up on the 32" TV and when the machine finally boots, the other two 24" monitors work and the 32" disappears from the scene. I look at the Display arrangement window and it only shows the 2 x 24" monitors. Very strange as it is obviously seeing the 32" as well, but drops it off when the boot completes. As previously mentioned, it had all been working beautifully prior to the system crash. It is driving me mad. I can't find a way to make it work, but it occurs that it would have to be a software issue as it does see all three, just not all together. Anyone with any ideas? They would be most welcome indeed....Cheers