It's mainly in Saint Denis and Valentine. The worst areas for the amount of glitching and hanging of all are near the Church (the larger one) in Saint Denis, outside the Saint Denis police station and the stables and entering Valentine. I think that it's the less CPU intensive areas seem to be less affected.
When I first start playing as long as I stay in the wilderness. The RAM increases around Valentine and Saint Denis though. and once it hits that 10gb mark (usually in 5 or so minutes of riding around if I'm in Saint Denis) then bam! Stutters and hitching. The VRAM also fills up to the 7.5GB max if I have almost all of the settings all maxed (at 1080p), but even if I don't and the vram is lower, the system ram still builds up to and then dumps that half gig at around 10gb in the populated areas. I've tried everything with the page file, including system managed, setting various manual parameters and disabling it all together. Nothing works. Limiting the FPS, Vsync off/on/half, various launch arguments, Vulkan, DX12, async compute on/off, installing it on different drives (nvme and 'regular' ssds). Nothing.
I'm pretty sure that it has something to do with the game freeing up ram or something to load new assets, but I'm damned if I know why it would do it at the 10gb mark on a system with 32gb of ram. I tried Rockstar Support of course, but, well you know how that goes....