GPU memory is usually the in game settings for anti aliasing, post processing, and texture quality, rather than the Control Panel settings, which are usually defaults and can be overridden by in game graphic options.

Your low GPU Load is probably because it is spending all it's time swapping things in and out of memory. Reduce the in game graphics quality settings and you will probably free up some memory.

Other factors are which game you are trying to multibox and at what resolution. If you are playing at 4K, then multiboxing that on anything less than a couple of 980TI's or TitanX's might be tricky.