I suggest you capture a brief video with MSI Afterburner running. Set CPU, GPU temps, and Usage % to show onscreen while recording. Also set min and ave FPS to show. Also set VRAM and RAM to show. Post the vid here so we can take a look at it to try and determine what's wrong. Make sure to make the stat fonts in Afterburner big enough to easily read while watching the vid, as we need to know at what points the spikes are worst.
Did you use the built-in game benchmark to determine graphics settings? It's pretty straight forward and easy to use, and is even color coded. Any settings that don't show a green text bench result cannot be trusted to yield stable results. Also, definitely let us know ALL graphics settings you're using. I recommend having Vsync, FPS Limit, and Adaptive Quality Off, with Borderless Window mode.
Theoretically that spec should run the game, IF your settings aren't pushing it's capabilities too hard. You didn't mention what RAM you're using.