So a couple of weeks ago I was running Skyrim on Ultra quality with 2k textures mod. Then I messed up the files somehow in my Skyrim folders and the game did not run right, so I uninstalled from steam and deleted every single file to get a proper uninstall. Once redownloaded, It will only NOT lag on low quality, with no mods installed. I played on vanilla ULTRA, and it took my game about 5 minutes for loading screens, and serious lag.