My phone gets really hot when playing games. I've tried throttling the cpu all the way down, but it doesn't seem to help any. Is there anyway to manually throttle the GPU?
My phone is an LG Motion 4G LTE
Most modern smartphones produce a lot of heat when playing CPU/GPU intensive games, there's not much you can do about it.
If you reduce GPU frequency, two things can happen: stuttering of gameplay (depending on your game), and the CPU/GPU run at maximum frequency for longer amounts of time to complete the same work (that a higher frequency GPU would have done in shorter time). That may negate much of the heat reduction you are trying to achieve. My 2 cents is to leave the settings at stock.
(for more details, read http://forum.xda-developers.com/showpost.php?p=34153152&postcount=15576 by a chip designer who worked with Nvidia, TI etc).
If you are still keen on underclocking, http://forum.xda-developers.com/showthread.php?t=1827635 suggests that GPU over/underclocking is possible with SetCPU app. That link is for Galaxy S3, but it should work for your phone too if your kernel supports it (you might have to flash a custom kernel to control the GPU).