my premiere pro proper not using my gpu

I don't know what processing is going on at the time. The GPU is not "just an extension of the CPU" but an entirely different subsytem, used for different things. Premiere is coded to use the GPU for those things that are internally coded to use the GPU. And it doesn't 'generally' use the GPU for everything.

So ... what media do you have, and what effects used, and what codec are you rendering to? As all of those can have an effect on where bits are processed.