Matt, I’m Using the Decklink for Video and Audio Playback. Also I have it set in premiere as “Blackmagic Audio”. Im using the XLR outs. Also Im monitoring with HDMI and HDSDI. I have had the same issue on Cannon DSLR H.264 Footage, RED Scarlet R3D Footage, XD CAM Footage, and ProRes 422 (all flavors). Most everything has been on a 1080p 23.976 timeline. We shoot everything in 23.976.
I think that answers your all your questions.
-Kyle
Live, Life and the pursuit of Pixels