How to make Hierarchical Clustering on GPU?

We would like to classify more than 2000 observations by the cluster hierarchical method. We did it by using the CPU and Matlab built-in functions (pdist, clusterdata etc) but the calculation with the CPU takes a really long time especially when the amount of samples is really big. We would like to do this clustering by using a GPU instead of the CPU in order to speed up the calculation. We are beginners in using the GPU but we have read how to use it on internet. We have tried to make the cluster calculation on the GPU by using Matlab but the calculation time is longer than on the CPU. Could you tell us if there a solution to use the clustering analysis with GPU with Matlab which would work faster than CPU? We don't want k-means for the cluster because it is not precise enough.