Can't solve frame pacing issue.

[evilmeister13]

I recently picked up an msi ge62 apache pro from a local pawn shop for $500, configured with a core i7 5700HQ 2.7Ghz and a GTX 960m 2GB with 12GB of ram. I fired up Rainbow six siege, my main game, and it has just awful frame pacing, the game feels lurchy and gross to play. I'm getting around 45fps, which is what i expected at low settings, but it doesnt feel that smooth at all, movement is jerky and near impossible to control and it gives me a headache to watch. I tried lowering my resolution to 720p and setting render scaling to 50% of that, all to avail, no boost in framerate or smoothness. I then fired up fortnite and had the exact same experience. After a bit of temp monitoring, I figured out the issue was my cpu hitting 90 degrees and dropping its clockspeed down to around 1.2GHz. I opened it up and cleaned it out, verified the fans were working, cleaned off all the thermal paste and replaced it with thermal grizzly kryonaut, and it did nothing to affect the temps. I then updated the bios, as that seemed to help some people, but it hasn't helped me. I then tried undervolting using both Intel XMT and Throttlestop, but was unable to affect my temps that way either. It's quite frustrating as it makes any game completely unplayable. Any other ideas on how I could solve it?