Freezing when in 24M instances

[Hozin]

Hey there, I am having some issues that i would like some help with if anyone has similar ones, i can run the game on max everything at 110 fps when standing still 80-105 wen running and 50-70 when fighting in a instance that does not have a swarm mobs, so basically i run the game pretty well no stuttering problems and such. Two problems i have are the freezing that occurs when in a 24m Instance when i have to fight the main boss may it be The mysterious Man or Poharan, I could have fought Poharan with little to no freezing now that i think about it pre-patch but now the game just freezes. The second problem is when am doing PvP dalies and persons are farming the terrors if i am anywhere in the area and they drop to my channel i get an fps drop when am not even there vicinity. It has become really stressful as i have been there for the third time trying to kill the mysterious man to no avail i even went as far as to put my resolution down to 800x600 and all the settings to low but still the game froze up. Yes and i run the normal 6m versos of these instances just fine no problems

Specs: AMD Phenom II x4 965 Black 

Evga Gtx 660 Sc

6Gb Ram

TL;DR: The game is freezing when i fight the main bosses of the 24m Instances and i am looking for a solution. A better explanation is in the passage.

Thank you for reading any help would be gladly appreciated.