Did you make any major graphical changes in the game or the Nvidia settings for all programs?

Do you use mods?

Does this happen on new and/or old save games?

All I can suggest is trying to redownload the latest drivers from nVidia. Failing that, if you use steam, do a integrity check on that game.

If it is your  graphics card trying to take early retirement, you should try some other games, high end demanding ones. If they’re all fine, then your gfx card is probably OK. If not, you may need to return it/but a new one.

Graphics cards can be highly unpredictable with their life spans.

What’s the maximum temperature your graphics card runs at while playing TF?

It’s best to get these things returned asap if they’re buggered, especially if you got it online.

Just fyi, My somewhat ancient AMD Radeon 6870 1GB has no issues what so ever with tring fever.

I assume you’ve assembled the PC correctly, and have the required power being supplied to the GPU. I made the mistake of only connecting 1 of the 2 PCI power connectors a while ago, in my haste to rebuild my PC, that had some pretty odd effects. Luckily it hasn’t done any damage!

There’s a stress and error checking program called OCCT you should take a look at.

Also check you’ve seated the card correctly, usually it just won’t work at all, but sometimes can give wierd artifacts like you’re seeing.

Hope this helps! Sorry to keep saying it might be your card, but new cards can be just as unreliable as an old one in my experience! (I’ve had to return more dead new cards, than replace dead old ones!)