For me the stutters seem to be only when i move around and the game is loading in new things and loading out the old things. Try lowering render distance, that decreased my stutter a bit, but i still get it when sprinting through forests.
But that save lag is absolutely brutal, it has gotten me killed many times. From what I've seen, it has to do with the fact that the game doesn't allocate more ram to itself when it is saving. There's a mod that supposedly fixes the issue by allocating more ram to the game, but i haven't used it because i'm not chancing my save file getting corrupted.
There's also a confirmed problem recognized by the devs that when the game removes old data from memory that it causes a lag spike, that's the 1 to 2 second lag you get every 5 to 10 minutes, apparently it is an issue with unity itself.