Which overlay are you talking about?
What is the Version of LR you are using?
GPU acceleration works on some computers and not on others. If everything works fine with GPU acceleration deactivated then that should be the setting you should use. The feature does not make everything in Lightroom automatically faster. I don't have a dedicated graphics card in my computer. But it is my understanding that the main benefit for having GPU acceleration is for those users who have high resolution monitors.