[SOLVED] frametime issue- thermal throttling on GPU?

hey everyone. My dad (who tries to be weirdly "hip and cool with the kids") was playing fortnite on my PC just now, when he started to complain about stuttering. The framerate stayed above a solid 90 (60 in some areas high-density rendering areas such as tilted) but at some points the framerate didnt look like it was 90. I ran the MSI afterburner overlay, and saw that the frametime was between 10-30, but usually around 12-15. Sometimes it would spike to 30 for a quick second, but it was noticeable. Ill supply a parts list, but the 3 front fans on my case don't work. I bought some good thermal paste to use on the CPU stock cooler so it wouldn't get crazy hot (don't worry, I haven't seen the cpu get above 60 under 100% workload) and a replacement case and fans are arriving tomorrow. The highest ive seen the gpu during load is 75, but that isnt crazy hot. I set up a fan curve for my gpu but it gets CRAZY loud, so I disabled it. Here's the parts list:

https://pcpartpicker.com/list/DFCf4q

I have a 75Hz 1920x1080 monitor.
 
I'd recommend running GPUz and logging to file while gaming so you can see what's happening during the cuts.

If your GPU is anything like my MSI RX480, the target GPU temp is 75C. Are the GPU fans running at 100% speed? Knowing that you have zero intake fans for the case (none work?) if the GPU can't keep itself cool by speeding up its fans, it will throttle itself down.
 


When I’m running super intensive stuff, I’ve seen it get to 60% fan speed and that’s it. It stays pretty cool. If thermals aren’t the problem, what could be the problem?