game stops lagging at the end of the game

Hey guys, i dont know if anyone else has this problem, but everytime i have lag (100-100.000) enjoing the game, at the last moments(which usually cant turn the side of the game) it drops to 60-80,which is really frustrating since i get used to not knowing what happens in the first 25-30 minutes of the game and that changes drastically in the end. Can u solve it rito?