I know that sometimes i have removed ram or vid cards only to find that it fixes the situation as they get unseated somehow. ive had ram be reseated 2-3 times and then the whole mess gets cleared up.
This seems a vid card situation and i almost want to say your grafix card is goin out, that would make it crappy with all games though and as its only with DoD you say......if its not happening with more intensive games im at a loss.
honestly this just happened to me on Civ V so i had to turn down the grafix and that got me goin smooth again. but im not running an old card. just built this pc this year. so i lean towards my card is fine just not ramped up enough to run the game smoothly cranked up.
the only other thing i can suggest is watch your heat as always. perhaps you getting in intense fighting with smoke and heating up the card. age would make this more prevalent.