I found these suggestions on a forum help
1. Disabled Multi-Core Processing in tf2
2. "optimized" multi core processing in tf2 (added like 5 lines of code to my autoexec.bat that apparently helped some people)
3. Set my settings to as low as they can go
4. Checked if video card was overheating during game play
5. Ran a multitude of memory checks on RAM
6. defragged hard drive
7. checked integrity of tf2 through steam (an option if you right click tf2 in Games)
8. updated drivers to newest
9. downgraded drivers to an older version
It might be your graphics card overheating?