Use of GPU technology is limited to certain types of analyses. At present, only 3D Fill+Pack analyses support GPU technology.
The analysis you run is restricted by the size of the available memory on the GPU. For example, if your GPU card memory size is not large enough to run the full model, then the analysis will use the GPU for smaller time steps when the model is partially filled.
When running computation-intensive tasks on a GPU card, the card will be diverted from other tasks such as redrawing the Windows desktop or refreshing other applications. This can be especially noticeable when running multiple jobs simultaneously or when running a very large analysis.
The latest drivers for any installed card will need to be updated.