Figured out the Shift key issue with Passthrough and Broadcast mode. GCP intercepts the Shift key even if you are in these modes if it is not the active program in Windows. So If you go into passthrough mode for example and then click in the game, then try to type Shift will be intercepted. If you then select GCP again as the active window it will no longer be intercepted.

If your able to fix this in a future release that would be cool.