So I just built this new system off of items from PCpartpicker. It is my first time building or even using a pc so I had some trouble at first but finally got it running. Whenever I go to launch a game the FPS counter is always above 150 frames, but after 3-5 minutes my gpu stops using its power on the game, and starts forcing the load onto my cpu giving me consistent 70-80 FPS but it is extremely choppy, however, when the game is in windowed mode and I alt tab it quickly jumps up to normal FPS and my gpu begins running the game again according to task manager. I have uninstalled GeForce experience, turned off Xbox overlays, disabled G-sync(In Nvidia control panel), Changed optimization and prioritized my games in graphics settings,and reinstalled my drivers multiple times. Nothing I have tried so far has helped. I don't know if its worth mentioning, but I also have a, from what I've gathered, "faulty" stick of ram that is hardware reserved in my system. None of my games require more than a gigabyte worth of ram so I don't know if it's something to worry about.
Here are the Items I bought: https://pcpartpicker.com/list/QTZgD2