AgentVictor

ALRIGHT, I FIXED IT.
I did three things, but I am not sure which one of them was the life saver. I installed RAGE Native UI, I installed Albo's dll, and I also renamed the main folder's name to Grand Theft Auto V. This worked for me, at least. 

I am having this problem myself, as you can see in the picture, that's the result after I quit the game. What ticks me off is that I have turned off all possible AV software, and above all, have tried the fix they provided in that link to the RAGE website 3 times, to no avail. I am not even sure what's causing all this. All my files are unblocked, so there's no question on that behalf. What could possibly be causing this?!
Worth mentioning is the fact that this a clean install of GTA V; I uninstalled the previous one and just downloaded it from Steam, naked, about 4 hours ago. Maybe I am missing out on something? Not sure - but it sure as hell is an unexpected problem. I installed LSPDFR just as I did last time, which was also (what a word game) the first time. 

If you use ShadowPlay you can try disabling that whilst running GTA V, I found that caused a lot of stuttering, but it's more than likely just the game. Over the past few updates I've seen my FPS drop more and more and stuttering become a lot more frequent.

Reinstall your Scripthook and your TrainerV 

You will need to set PostFX to High or Ultra and Shaders to High in the in-game settings and you should be good. @AgentVictor

That makes sense. I'll try it out and report with the results. Thanks a lot!
Great looking out, mate. Thanks a lot, works like charm! Of course, I will play with the graphics settings a bit because I dislike the now low framerate, but that I can figure out myself. Thanks, again! Wish you a beautiful day!