You may rely on CUDA version installed for your current L4T version. Other releases may not work as expected, as this is tightly linked to GPU driver and X server.
Be aware that in general, opencv imshow may not be that efficient on jetson. You may try to boost your jetson with:
sudo nvpmodel -m 0
sudo jetson_clocks
You may also try to use an opencv videoWriter instead with a gstreamer pipeline to a displaysink, such as here.
Otherwise, for displaying from GpuMat, you may try to use an opencv Window with openGL flag, but this would either need an opencv build with GTK2 backend or QT4 backend