I have the same problem. I am running a 1070 in my PC and whenever I am rendering or even just scrubbing through footage, premier is mainly using my memory (32gb ram) but my GPU sits between 0% - 10%. At times It makes it Impossible to work on linked after effects compositions (if enough effects are altering or manipulating the footage). BTW I have GPU acceleration (CUDA) on of course, but yet Premier doesn't utilize my GPU. I believe it comes down to Adobe not having their shit together. I have seen videos comparing GPU usage between final cut and Premier and final cut actually utilize the GPU when rendering and scrubbing. When rendering in Premier Pro it hardly uses any GPU and is mainly taken on my the CPU maxing out at 99%. I think every one just needs to complain to adobe about this ridiculous issue. I find my self resenting Adobe more and more every time I use Premier and face these ridiculous issues... and I use it EVERYDAY. Adobe is trash until they can get up to speed.