You may want to consider looking into the Terminal command pmset. You can read its manual page by typing man pmset in the Terminal app. It uses the same files as System Preferences to configure power related settings but offers more options and granularity along with various useful logging features/stats. It might be helpful especially if you ever notice your power settings have adjusted themselves...
For example, pmset -g will show you your current configuration. If gpuswitch is set to 0 you would use your dedicated graphics processor (not the integrated one on the CPU) all the time regardless of your power source.
Setting it is easily done with:
sudo pmset -a gpuswitch 0
and you can add other settings in there like the added security of deactivating ttyskeepawake and even wake on magic packet/wake on "modem ring" (network can send a well known data file to wake the computer up from sleep which almost certainly keeps a port open to listen for the magic packet at all times):
sudo pmset -a gpuswitch 0 womp 0 ttyskeepawake 0 networksoversleep 0
gpuswitch can be set to 0, 1, or 2 and im not at my computer but can assume:
Some people think the average user isn't capable of using the Terminal but they can safely be ignored.