Ok, so I stripped it down this weekend in the garage and found some issues.
Number one was the gear selector itself, I took that apart, and it was an absolute nightmare of rusty water, mud, and anything else you could imagine. I cleaned it out along with all of its small internals and put in new ATF fluid for the lubricant. It now moves freely and shifts smoothly. Time will tell if the internals will need to be replaced but as of right now, it's ok.
Number two is the linkages that connect the selector to the transmission. The long one for both HI and Reverse had a considerable amount of washers on the end where the nut meets the tie rod. After loosening the nut and moving it back, I discovered that the washers were there because someone had stripped the threads on the rod. Due to this, I can't tighten the nut and properly adjust the rod. This makes sense as to why the shifter would occasionally pop out of high gear because it's not properly adjusted. I also discovered that the rod for the LOW gear is welded at the nut and the end rod. So I'm now either on the hunt for new/used linkages, or I may be able to re-thread the end of the rod.
Number three is that my driven clutch appears to be out of alignment. In neutral and at idle, the belt is sticking to the sheeve and constantly turning itself and the driven clutch. Due to this, I've ordered a real belt (Chinese one on it right now) and a package of shims to align the driven clutch properly.
Still unsure of why it was dying in gear that time because it hasn't happened since however I'm assuming some combination of improper adjustment of both the shift linkages and the driven clutch was the reason.
As I said this is the first Polaris ATV I've owned, and I'm new to the whole CVT transmission. Although it's a pain, it's still been a fun experience learning about these mechanisms.