New Dell g3 3590 having strange performance issues

So I have recently been seeing issues with frame rate and performance on my recently acquired dell g3. When I first get into a game, it usually runs at the top 60 with v-sync on. However, a little bit of time in, and the frames will suddenly drop to a low 40, sometimes to 30. For some reason, using the G mode key temporarily fixes this problem, but only for it to return moments later. It's then a rinse and repeat issue.

I have tested this issue on all of the games I currently have, and it's the same problem with all of them, even with optimized settings. I tried messing with Alienware cc, the Nividia settings, Power preferences, everything. And so far, absolutely nothing has worked. Is there even a way to fix this?