I've started two games in GS and both start becoming progressivley sluggish around 1300's-1500's. Both games on standard size maps with the default number of rivals/city-states. Graphics set low, where I always play games - which what made this issue so noticeable. Excerpts from my Aspyr support ticket. They responded, asking for additional details per SOP. Sent them a couple save files as well. Gathering Storm becomes extremely sluggish after about 15 minutes of gameplay. Units respond poorly to commands; delayed action and jerky. Can provide a save if helpful. Feels like it may be a memory leak. I did play a save from R&F and it played smoothly, as designed. When loading and playing a late-game R&F save file everything renders quickly, as designed.