I didn't assign SHIFT+3 to open the GPS panel.

By default it works like this:

Window00 = is opened using SHIFT+1 (in the CS B-52 you won't see anything).
Window01 = is opened using SHIFT+2
Window02 = is opened using SHIFT+3 (The GPS is Window03=GPS so SHIFT+3 opens it)
                  As each windows is added, the next SHIFT+n opens it up to:
Window08 = is opened using SHIFT+9

There could be a way to do it for greater number of windows, but the only time I have seen that done, is in the Flight Sim Labs Concorde and I don't know how they did it.

Mark