So I had an extreme issue with vertical lines, trails on movement and other artifacts on loading a save game (any save game) but not on a new game. I had done everything that has been suggested (lowering graphics settings, clearing cache, updating graphics drivers, validating the game files even reinstalling the game) and this didn't start until I hit 300 hours of game play. On starting a new game (again) I noticed that some items I had bought in a previous save showed as being added to my inventory but was only a few minutes into the game and they never appeared in my inventory. The items in question were bought just prior to making a save game and quitting. Apparently the items never finished being added to my inventory and for some reason it was picking this up from the old save when I opened the 'Load Save' screen. After deleting the saves from that point on (including autosaves) it fixed the issue with the graphics and the game trying to add the items to my inventory. I have no idea why something like that would be picked up from another save game that was not even loaded.