Lag issues and problems with FPS

[Vextren]

My specs are really good but on GTA V (the only games this occurs on) it goes from 60fps (V-sync is on) to 2fps all the time. I have seen people experiencing this every now and then with slight stutters but the game for me is unplayable, i have a link attached to an MP4 showing how bad it is. The thing is it is not hardware because of my specs (Linked below with the link to the MP4) but i think it may be software or i am missing something. I have verified the integerity of the cache files in steam and checked for updates for my video card from the geforce app but nothing. even used dxtory even though it was rendered useless with windows 10. I have also tried running compatibility mode in windows 7 and 8 and ran GTA V in directx 10 and 11. Also can I confirm I only just purchased GTAV this is my first experience playing it and it has been only this so this is my only result of playing the game and not a new issue its been like this since yesterday when i downlaoded it.

Video link: https://support.rockstargames.com/attachments/token/iPGRf3fDI6UcOyebTophvp1oO/?name=Untitled.mp4

Specs:
CPU: Intel Core i7-6700K 4.0GHz Quad-Core Processor
CPU Cooler: be quiet! Dark Rock Pro 3 67.8 CFM Fluid Dynamic Bearing CPU Cooler
Motherboard: Asus Z170-A ATX LGA1151 Motherboard
Memory: G.Skill Ripjaws V Series 16GB (2 x 8GB) DDR4-2400 Memory
Storage: Samsung 850 EVO-Series 500GB 2.5" Solid State Drive
Storage: Western Digital BLACK SERIES 2TB 3.5" 7200RPM Internal Hard Drive
Video Card: Asus GeForce GTX 1080 8GB Founders Edition Video Card
Case: Phanteks Enthoo EVOLV ATX Mid Tower Case
Power Supply: EVGA SuperNOVA NEX 650W 80+ Gold Certified Fully-Modular ATX Power Supply
Operating System: Microsoft Windows 10 Home OEM 64-bit

 

[hang-the-9]

Test the system with a benchmark like 3DMark, compare your results with benchmarks for your video card, see if they are inline with what they should be.

Also make sure your game is patched. Make sure there are no heat issues with the system.

Other games work OK?

 

[Vextren]

Test the system with a benchmark like 3DMark, compare your results with benchmarks for your video card, see if they are inline with what they should be.

Also make sure your game is patched. Make sure there are no heat issues with the system.

Other games work OK?

My PC has ran all other games great, I have used MSI after to turn up the GPU fan speed by 65% and all other games worked fine before hand except battlefield 4 which made the pc get a bit hot and one time crash but fan speeds have been increased, game has had all steam updates and I have verified the integrity, even ran it on the lowest settings and recommended for my system and nothing.