After many hours of debugging, I finally figured out that the DeviceInterfaceGUID for WinUSB devices was not being installed *only* when plugging the device into USB 3.0 ports on the Win7 machine. With that information, I finally found this thread:
http://www.microchip.com/forums/m802958.aspx
That thread solved my problem, and hopefully it will help others in this same situation.
http://www.microchip.com/forums/m802958.aspx
That thread solved my problem, and hopefully it will help others in this same situation.