Also, GPU usage in what?
For games, disabling V-sync will result in higher FPS, but may exceed your monitor's refresh rate and result in tearing. Also you can increase visual effects and resolution to increase GPU usage.
A GPU not running at full speed is usually a good sign. It means that whatever you are running is going as fast as the settings allow and your GPU is running with less power.
It can be a sign that your system doesn't have enough of another resource to run the game faster. Usually the CPU would be the common culprit. Many older games are single threaded or still rely on a master thread to control all others. As fast as that thread can be run is as good as it will ever get. These are known as CPU bound titles. Usually...