A couple things: Verify the temperature. If may be that you have faulty cooling. Use a program like speccy or other to see what it is during game. Use steam to verify the game files to ensure it is not an issue with that. Is the lagging consistent moments? Try changing the graphic settings as sometimes severely high lighting settings have weird issues. Maybe other users with the same card can shed light on if they are having similar issues that would relate to a driver issue.
Also to throw into the questions, what monitor are you using? This is a big thing with the 1080Ti is that it is made to be played 2K and up. What PSU are you using? We will need specs or your whole PC.