So I have a four year old computer. I haven't upgraded it's CPU, which is an i5 2500 (3.30GHz), but I've upgraded it's RAM to 8 GBs and it's GPU to AMD's R9 380 Sapphire 4GB. While playing Dishonored 2 with the visuals at Ultra the game runs just fine. However, at times I get some HUGE FPS drops, or maybe I should say lags. Basically, for a sec or two the screen freezes. They don't happen often enough to break the game but still it's not that good. The CPU is at 70-80% during most of the game, but at the beginning of said lags, the CPU usage drops to 2-8%. After a second or two when the lag finishes the CPU usage goes back up to 70-80%. So are the lags caused by my old as hell CPU? If so why? Aren't games mostly run by the GPU?