2 external monitors with iMac 27

I have two monitors and am trying to figure out if i can get the 3 screens to work independently.

Current set up

Left: External monitor (hooked up to thunder port)

Center: IMAC 27 inch

Right: External monitor (hooked up to thunder port)

I have been use the center and right for a long time and just added the left one.
Currently it looks like it is just an extension of the middle monitor.

Is there a way to make all act independently. From the settings option it looks like they are all independent. So my questions:
1. How do I make them all independent
2. can I make it so the mouse can scroll left to the left one and right to the right onw.

Make sense???

Ok..actually it looks like it is working BUT it is really slow to get the cursor over to the external monitors....and back. So it looked like it wasn't going.

Anything that I can improve that with. (even if i had to pay for something - inexpensive).