Stuttering Issue with Games

Okay so this is going to be quite the post but I'll include everything I can. In July I picked up a computer off of Newegg (link to actual computer for a decent price. It runs great and everything except when I played Counter Strike: Global Offensive, Total War: Shogun 2, and XCOM: Enemy Unknown.

What happens is when I get into the gameplay it starts to stutter. It doesn't matter how high or low I turn the graphics to, it still stutters the same.

So I decided to invest in an AMD Radeon HD 7700 Sapphire because I thought it was the graphics card itself causing the problem. Once I installed it and updated the drivers, I booted up XCOM and low and behold the same exact stuttering problem. I honestly have no idea what it could be now. Maybe the motherboard? Here's what I've done to try and resolve the situation thus far:

• Updated drivers, windows, and changed out AVG for Window's Security Essentials
• Validated files on Steam
• Checked temps through the Fur Test, they stabilize at 68c and idle at 34c
• Used driver sweeper to remove NVidia drivers from my motherboard (recommended from the support chat)

I'm open to any suggestions, or if anyone knows what the problem and solution is that would wonderful. Thanks!

EDIT: Info on my computer: AMD FX-4100 Quad-core, 8GB RAM, 500gb HD, AMD Radeon HD 7700