Hey, so when the game first released I got to level 60 easily all went smoothly. Then 1.0.3 came out. Now I lag as soon as I go into combat, no matter what. Bearing in mind I played at full settings before the patch. I have 60 fps (Vsync on) or 100 fps (off) and whenever i go into combat it goes down to 5-10. Completely unplayable. I have a NVidia card.
It does this for me too but it only lasts about 5 seconds when I first start up Diablo. I just take it slow for that first part then go at it. I assume it's much longer in your case but I am not sure what could be causing it. I run BF3 on ultra and every other game I have tried(EVE, WoW, Skyrim, New Vegas, Crysis 2) still performs without any noticeable degradation of performance so I dunno why D3 does it.