Hi,
Using a GPU more than once does not make sense here. It would mean executing python code twice in two different threads and run twice as many ops on the gpu (which are half the size). And GPUs are really bad at running small ops.
If the GPU usage is already 100% all the time, then the GPU is fully used and there is nothing you can do to speed things up more from the code point of view. Of course reducing model size/architecture could.