Today I upgraded to 5.20. When I was using 5.10 I could stretch the piping input screen across both monitors and have the spreadsheet on one side and the 3-D graphic on the other. Now with 5.20 I can't stretch my input window wider than a single screen. Is there a way around this?

What you can do is pull the input spreadsheet outside your "input window" and place the input on the second monitor.
When moving the input spreadsheet - as long as your mouse does not come in contact with the margin of your "input window", the spreadsheet will not dock on that margin. So, use your mouse to shift the edge of the spreadsheet outside the input window. Then click and drag the spreadsheet from a point outside the input window and locate it properly on the second monitor. The graphics will remain in the input window.
I cannot say that we have a reason to limit the input window size.

I also have 5.20 will dual monitors. One of which is a wide screen monitor. For some reason, the input screen cannot be maximized to the full extent of the widescreen (a gap remains on the right and bottom). I can stretch the window to fill the bottom gap but not the right side. 5.0 worked fine as well as other programs I use. Is there a way to fix this?

This appears to be a consequence of upgrading to a later version of the HOOPs graphics library. We are discussing this issue with the HOOPs vendor, and hopefully this behavior can be changed in the near future.

There is nothing you can do on your end, the HOOPs library (that we link into CAESAR II ) has to change.