Stuttering High End Build

[Whimsical Amoeba]

Hi there! Hopefully someone here can help me, if so I would be very grateful:
I've tried asking at Toms Hardware and on Reddit, people have been helpful and suggested things but nothing so far has worked

PC specs:
CPU: i9-9900k.
RAM: 16GB 3600MHz RAM (Crucial Ballistix BL2K8G36C16U4B).
GPU: Asus 3080 STRIX OC.
Other PCi cards: ASUS Essence STX 2 (internal sound card).
Motherboard: ASUS Strix Z370-F motherboard.
Cooler: ASUS Ryujin 360 AIO cooler.
PSU: Corsair RM850 PSU.
Peripherals: ASUS ROG Delta S wired headset, Steel Series Sensei TEN wired mouse, Corsair K70R wired keyboard, Wireless XBOX One gamepad.
Monitor(s): ASUS PG278QR Gsync Monitor, Acer VG270U Monitor(Bought to test if my other monitor was the problem)
Storage Drives: Samsung 850 EVO 250GB SATA, Samsung SSD 970 EVO plus 1TB NVMe, Samsung SSD 860 EVO 500GB SATA, Samsung SSD 850 EVO 500GB SATA, Samsung SSD 860 EVO 1TB SATA.

All Drivers are installed and are the latest available versions
Chipset Drivers are installed.

For several months I've been getting a periodic stutter in games. The stutter is intermittent and relatively rare in most games, Bizarrely one of the games that seems to work near flawlessly is Cyberpunk (I know, that seems counterintuitive. I still get a rare stutter though.. maybe once in an hour or two of playing) Grim Dawn stutters every few minutes, WoW 'hitches' a lot, Borderlands 3 is a stuttering s***show, Warhammer Total War stutters on the campaign map, but not visibly in a battle (though I have seen semi-regular frametime spikes), AC Valhalla gets a rare stutter, Sekiro stutters seemingly arbitrarily, Horizon Zero Dawn seems ok, but I haven't played it much since this started happening, RE Village stutters every now and then, Valheim gets a pretty severe stutter relatively frequently.
Before this stuttering started I had only known a smooth experience, so I know what gameplay is meant to be like and this is definitely not normal behaviour.
The stutters show in Afterburner as a huge frametime spike (>100ms huge). Ive tried without Rivatuner or Afterburner installed though and the behaviour persists.

The system scores roughly where I would expect it to on 3dmark, User benchmark says "performing well above expectations" on everything it tests.
Unigine Heaven has the large framtime spikes with scene changes and a reproducible stutter/frametime spike when the camera spirals down toward the dragon statue
Unigine Superposition benchmark is mostly stable but still has spikes (these dont result in a stutter though).
OCCT shows no errors, PC passes the power test and the GPU / VRAM tests with no issue
Memtest finds no errors on the RAM.

Things I've tried:
Tried 3 different GPUs after assuming it was the new 3080; a 2080 and a 1080.
Replaced motherboard (from the Asus z370-f to an Asus z390 Prime-A and back again),
Replaced RAM (4 different sets)
Removed SSD's removed m.2 drive,
Removed Soundcard
Removed headset,
Clean reinstalled windows countless times on different drives, inncluding trying Winndows 11 (I was/am desperate at this point)
Replaced CPU (from an 8700k),
Replaced PSU (from a Corsair TX850m)
Replaced Displayport cable (several),
Tried with and without Gsync
Tried without being connected to the internet
Several sets of drivers for GPU, tried with ReBAR on and off, tried several different BIOS versions on both motherboards, tried several different bios versions for the 3080.
Tried three different mice (two corsair mice and now the Steel Series I'm using) and two different keyboards.
Tried taking the PC to my parents house (several miles away)

Still have the same intermittent issue.
If anyone has any insight or clue as to what the problem might be, please help, I would be most grateful.

[emosun]

according to what youve said , you already replaced the board , gpu , ram , drives ,and cpu which means the entire machine has been replaced and you claimed to reinstall windows on multiple drives which means the software was entirely replaced.

You haven't however described very well what constitutes a stutter at least for you which may indicate your expectation for a machines capability might go beyond what is to be expected of normal operation. having replaced every single thing in the configuration that likely hood is very high.

what is it exactly that you are expecting from a computer if you can elaborate on that

[Whimsical Amoeba]

Hi and thankyou for responding!

To elaborate on the subject of reinstalling Windows; I formatted each drive to make sure I wasn't carrying any software issues over. I've used the 250GB SSD as my boot drive, I've also used the m.2 drive as my boot drive, I've tried only having those drives in seperately by removing the other drives. Including having only the m.2 drive installed with no other SSD's connected, and visa versa.
This wasn't on the first attempt at resolving the issue, I've been troubleshooting this PC for months. Windows has probably been reisntalled a dozen times now with different configurations of hardware to eliminate every potential culprit I could think of.
 

I'm not sure how to describe the stutter in a way that translates well in to text, though that's totally on me.

Whatever I'm playing will just freeze for a half a second or so (it's probably a fraction of that, but feels like an eternity when you're playing something fast paced like Doom Eternal. it's not a dropped frame, or a subtle skip that you have to look for, it's immediately noticable when it happens. in Total War: Warhammer 2's campaign map it's almost like network lag I guess, except it's not an online game. With Borderlands 3 the game is  pretty much unplayable, Sekiro's stutter is strange in that it is quite rare and seemingly arbitrary, so it might not be related to whatever the issue in this machine is.

Again, thankyou for taking the time to read/respond!