Im having the exact same issue. I play farcry 5. when the game starts, its running at 60fps. but right after 10mins when the gpu hits 75 degree mark, it starts throttling back to about 1020mhz. 75 degrees is quite safe temp for laptop standards and does not require throttling. Dell really needs to fix this issue.

ohh and as a cherry on top, my msi afterburner OSD doesnt show up either, tried numerous fixes but no luck (i have it up and running on my two other radeon laptops so i know how to set it up)

I have had enough of Dell's **boop**ty support. They have no idea what they are doing and I am sick of sending my laptop back. It is up to the community to help each other. I have had better luck researching and fixing these issues my self than going to Dell support. If it were up to me I'd return it and go to something different. My 7577 does not run like it should and I can't tell you how many issues I have had with drivers and software causing issues with audio, etc... 

Hi i also noticed that im getting clock speeds of only upto 400MHZ while playing witcher 3 after like 10 mins of gameplay 

bro  i had the same issue  just disable turbo boost from   bios settings (i know it hurts sacrificing cpu  clock speed ) but it wil lresolve  the fps drop but the  gpu temp limit won't get fixed till  dell makes a bios update to change the  current   max gpu temp limit 

Hi guys
If you want to change the limit for your gpu i have found this handy little program called gpu tweak 2 by asus
https://www.asus.com/us/site/graphics-cards/gpu-tweak-ii/
Now before anyone says that it wont run on dell i have used this program on my friend’s dell g7 and i can take the temps to 96 digrees now it was before locked at 77 digrees
However this did not fix my problem as his temps are still going to 96 digrees which is way too hot and it still throttles when it reaches 96
FYI the laptop is a 7577 dell g7 gtx 1060 max q and an i7 8th gen
Today i tried locking his voltage curve in msi afterburner to 1250mhz at the least volts msi afterburner gives you and his temps stayed at 85 for the gpu and 80 for the cpu
We were playing gta online at the time for around 2 hours
And i have also underclocked the cpu to be at 3400 mhz for all cores and given it a 120 mv undervolt from throttlestop
Along with removing the tick from bd-procshot or something like that and turning on speedshift and putting its value to 0
Try this i hope it helps

i forgot i have also changed the thermal paste of the laptop for both gpu and cpu, this was my first choice but it did not fix the gpu throttling though it did make it better for a few days but it came back