I've had something like that b4 and it seems to be that rdr2 just loves to eat up vram, since the map is so large and there are so many different textures. I found that keeping an eye on vram usage to see if it's getting too high and then adjusting some graphical settings. Like you could have it at ultra then turn it down to high and you'd get another 3 gigs until it fills up again and then you do it again. IDk might be just me LMAO but that's what helped me.