GTA V - task manager shows 100% CPU usage, but not really

[Musk]

So here's a thing - when I launch GTA V, even in main menu task manager says the CPU is used 100%, all the cores, all the time - but actually it's not true!
I know how loud my CPU fan gets and how much the CPU heats up when it's under heavy load, and this is not it. In task manager, in both "Processes" and "Users" tabs I found that even though it shows 100% CPU usage overall at the top, when looking at individual processes, I'm actually using around 50%. So what is going on?

I also have problems with the game itself. I have played GTA V back on Windows 7 a few months ago with no real issues. The game was using pretty much all my CPU (Core 2 Quad Q9550 @3.4 GHz) most of the time, but it worked well, usually 40-50 FPS.
Now, I installed the game again on Windows 10, and there's some wierd things going on :| Fixing some of them just introduces new ones...

At first the game was taking around 3-4 minutes when loading the saved game. Even though it's installed on an SSD and normally it took around 30 seconds. There was also a looot of textures not loading up. So I googled around, and learned that giving the GTA5.exe process higher prority solves this problem. I set it to "above normal" and it did help, everything was back to normal and working again. But I quickly found 2 problems with this solution:
1. Every other program I have running doesn't respond, since GTA is probably eating all the resources, having the higher priority and all,
2. the game or system crashes after some time...
(also, changing the priority every time I'm launching the game sucks)

So, since this solution wasn't vey good, I had to try something else. I started wondering, why the game loads for sooo long, and I found that for whatever reason, instead of loading it into RAM (I have 8GB, around 7GB is free to be used) tha game was using page file. Fricking page file! How in the world did Windows figure it's good idea to use page file instead of using all that free RAM?!
Well, whatever, I decided to shrink page file's size from 2GB to 128MB and see what happens. The game loads just fine, task manager says it's using ~3GB. Looks good. But then I get an error message, the one that shows up when you're using all your memory and it tells you to close some programs or they may lose data. Meanwhile, task manager shows I'm actually using ~4GB of RAM, half of what I have. Then after a few seconds it just kills GTA5.exe process.
:|

Well, let's see what happens when I disable the page file completely. The game loads fine. Suprisingly, no errors about memory usage. Performence is as good as usual, BUT, now textures take ages to load, there's missing buldings, streets, and after a while it freezes. Usually it just crashes at this point, other times it unfreezes and works for another minute then freezes again.

This is getting ridiculous, it worked just fine a few months ago on Windows 7, nothing changed except new OS. And I never ever saw task manager show different CPU usage in performance tab, and different in other tabs. Any ideas, guys?

I have legal copies of both Windows and GTA V (no mods installed), scanned the system multiple times with Windows Defender and Malware-Bytes Anti Malware - no threats found. I have reinstalled drivers and the game. The system is pretty new too, installed it maybe 2 weeks ago. I have a password protected Administrator account, and a regular user account I'm using. Running the game as Administrator doesn't change anything. I have no issues with any other video game or program.

My system specs:
MB: GIGABYTE EP45-UD3LR (LGA 775)
CPU: Core 2 Quad Q9550 OC @3.4 GHz (8.5 x 400MHz)
GPU: MSI GTX 960 GAMING 2G
RAM: Corsair 8GB DDR2 1066 MHz (5-5-5-15)
PSU: CoolerMaster G550M
The OS and the game are installed on an SSD.

 

[Trouble]

I would probably first check with the SSD manufacturer and make sure that I had the latest firmware update for that drive.
Then I would download the latest driver for the Video Card from here http://www.nvidia.com/download/driverResults.aspx/95559/en-us
I would then download this http://www.wagnardmobile.com/forums/viewtopic.php?f=5&t=135
Reboot the machine in safe mode and use Display Driver Uninstaller to remove the driver.
Then I would boot normally and install the latest Nvidia driver, using the custom button.
I would check the box to perform a clean install and I would uncheck everything referencing 3D and the nVidia Experience program. Leaving only PhysX and the nominal driver.

 

[Musk]

I checked the SSD, they never released any updates, it only has the firmware it comes with. And as I said, I already reinstalled the latest drivers, including GPU drivers. It doesn't look like it's fault of either SSD or GPU. Huge loading times where effect of game loading from page file located on a regular HDD, instead of RAM. And overall performance and framerate in the game are really good, at least when giving the process higher priority, though I didn't have to do that back on Windows 7.

Also, the main reason I wrote here is because of Task Manager showing different CPU usage than what it really is. What's the deal with that? It's the first time I saw something like this, and nothing like this happens when not playing the game.

I'll describe it a little more. In Windows 10 the Task Manager lists all the processes running, and next to every process you can see how many resources it uses (CPU, memory, hard drive, network), and on top of the list it sums up the usage of all those processes. And the wierd thing is, that when looking on the individual processes by yourself, the CPU usage sums up to around 50% when the game is launched, but for some reason Task Manager sums it up to be 100%. It appears on top of that list, and in "Performence" tab where it shows you graphs with usage of various components. And I'm pretty sure it's not really running on 100%, as the fan doesn't spin as fast as it should, and the CPU doesn't get nowhere near as hot as it should when hitting such heavy load.