Extremely choppy video playback while editing

Hey, I've been having an extremely frustrating issue and I'm not sure how to fix it. I'm a Twitch streamer, and I edit together videos from my stream VODs to YouTube videos. For quite awhile now, I've been having an issue with extremely choppy playback after I bring these videos into Premiere. They make editing an aboslute nightmare, as most of the time playback is a literal slideshow. even at 1/4 quality. Usually when I hit play the playback will start smooth before getting extremely choppy after 1-3 seconds. At this point I have tried EVERYTHING, tried solutions from every single "guide to eliminating choppy playback" that exists on the internet, and even went so far as to do a completely fresh install of the OS on my PC and completely reformatted my internal HD. The source videos are typically quite long (somewhere between 5-8 hours usually) but nothing I've read seems to indicate this to be the source of it. This is becoming increasingly frustrating and I really don't know what else I can do to fix it.

For reference, my system specs:

Macbook Pro (15 inch, 2018)

Mac OS Big Sur 11.2.1

Processor: 2.2GHz 6-Core Intel Core i7

Memory: 16GB 2400 MHz DDR4

Graphics: Intel UHD Graphics 630 1536 MB