I don't think CGS-D/PGS-D can be used for a Master's program -- from my knowledge they are degree specific. However, there is a master's award called CGS-M that is for your master's. I would recommend getting your CGS-M first as it will really help you get a doctoral level award later. Also -- If you start with a 1-year CGS-M, then transition to a PhD and you're awarded a 3-year CGS-D you will have 4 years of funding rather than just the 3 from the CGS-D.