Strange. Did you check to see if maybe it’s an Nvidia driver issue? Are you using the latest driver?
Your specs seem like plenty to run the game. The only thing that is really sub-par is the 5400 rpm hard drive, but unless the game is constantly loading from it, that shouldn’t matter. I have heard of bad ram causing issues, but I can’t speak about that since I have no experience there.
You should go into the task manager while the game is playing to see how much ram and CPU is being used, and also shut down all non-essential processes.