Okay so here we go:
This is an auros RTX 2080 super from Gigabyte I got sent after I RMA'd my first one due to it being stuck at 80c. Now that card took forever to get back to them due to mishaps in shipping etc, so I really don't want to go down that route. Instead, I signed up here to see if I can actually fix this myself. Since I'm so lucky, my replacement card is having a very similar issue! It was working fine for a few weeks when I got it, until suddenly a few days ago.
I bought this card from overclockers with a preinstalled water block on it (phanteks one) and its hooked up to a pair of 360mm radiators and a D5 pump. As soon as I launch a game, I can watch MSI afterburner or GPU-z and witness the same thing. The card will hit roughly 2Ghz, the temperature will climb, and it will rapidly fall in clock speed as it does. After several seconds, the card will be stuck at 1Ghz from throttling so bad, the power consumption will be low and the temperature levels off at about 74c.
As you can imagine, games are a sluggish mess and I can't play anything right now. My CPU is also linked in the loop (9600k) and temps are great even overclocked. I've tried changing the power cables on the card, reinstalled drivers, used DDU, reinstalled my copy of windows, and now I'm running out of ideas. I can't figure out what the problem is and I would really prefer this card to not have to get sent in shipping just for DPD to potentially lose it again. (Took a month until they sent me a new one)
I've added a screenshot of GPU-z when putting it under stress, what you see are the results within several seconds of loading anything. It's pretty constant after it gets to this point, though the temperature will slowly climb more after a while and I've seen the card get as low as 700mhz. I also tried changing the temp and power limit sliders on MSI afterburner, they didn't impact the results one bit. And no, there is no overclock on the card at all.
Last note: ignore the fan speed in the screenshot, idk where its getting that but all the fans are on pretty high blast. And as i said, its watercooled. no fans on the card.