MW3 Tech Help! All Your Problems Solved!

Launch the game and open up the Task manager (ctrl+alt+del), right click the MW3 exe and go to Set Priority and set it to normal. Play a bit and see if your problem is fixed.

If it is fixed, you can fix this permanently by going to config_mp in the mw3/players2 folder. Find seta r_autopriority "0" and set it to "1".