I have had KSP for years and just recently got a laptop with a 4k screen that I installed the game on. Everything was working fine for weeks, even with ~30 mods installed through CKAN. A couple days ago, the game started to run very slow and so I uninstalled the game, deleted CKAN, and reinstalled the game again. After the install was complete I ran the game with no mods and no ckan installed and upon entering fullscreen at 1920x1080, the fps in the menu dropped to 50-60 (as opposed to 120), and I could notice a stutter. In game, the space center was running at ~50 fps and in the VAB it dropped to 20. upon launching a Kerbal X, the timer stays yellow and my fps remains at ~20.
If I change the game to a windowed mode, on a resolution less than my laptops native resolution of 3840x2160 like 1920x1080, then the fps goes right back up to the normal 120fps that I had prior. As I increase the resolution, the average fps starts to drop. I normally play at 1920x1080 fullscreen all the time, because my computer cant handle 4k most of the time.
Of course I can physically play the game at a lower windowed resolution, but it would be highly inconvenient as the game is a small window in the center of my screen at that resolution. Again, this has never happened to me in this way before, and I have always been able to solve the issue by doing a clean install, but this time it doesn't seem so. Thanks for any help that you all have, and Happy New Year as well!
Specs:
Laptop: MSI GP62MVR 7RF Leopard Pro
CPU: Intel i7-7700HQ
GPU: GTX 1060
RAM: 16GB
KSP installed on 256GB SSD, but there is a 1TB HDD as well
Windows 10
x64 KSP 1.3.1, modless