if you are referring to the boot screen and things such as the boot picker (holding ALT to choose startup disk) then you will never have that with your GPU. They do not have EFI.
As to the other issues, how are you powering this card? The standard Pulse version will use both mini 6pins on your logic board and I know the Nitro+ version is more power hungry. It uses a 6pin and 8pin connector (instead of just one 8pin like the standard Pulse version). So I hope you are using additional power from SATA ports, or an external/auxiliary power supply......or have done some mod like the "Pixlas Mod" ?