The format, resolution of your media and details of your project including filters used, etc will all be important factors.
I'm assuming your 980 is 4 GB which is the minimum recommendation for GPUs in Premiere. A bit on the light side if you're working with 4k, or using a lot of filters.
Do you remember what driver versions you are using or have tried? You will need CUDA 9.2 or newer in 2019.
Updating to a 1000 or 2000 series nVidia card might not be a bad idea, though I can't guarantee that will solve anything.
I would also recommend the use of Cineform proxies for most users.
Thanks for the replies!
I am currently on CUDA 10, but I see a recent, new driver release that I can try to see if it helps the issue. I'm hoping that using proxies for my Sony a7sII footage eliminates the problem, though I have never had this issue in Premiere 2018.
I will probably eventually get around to upgrading the GPU as well.