Hey guys and girls

So got my hands finally on Dawnguard, and after I finished the first quest I did a quick save and then my computer started to lag.

I run Skyrim on the highest graphics with AA turned off, I also run it with mods aswell. Before Dawnguard this ran pretty well.

Before dawnguard I did have to remove saves from the save folder because it slowed down the frame rate but after removal of saves it worked perfectly.

This time though it's different. Loading times take forever and it the frame rate loss still persists. I've removed save files and it still is too slow to play.

I have turned off all mods and started a fresh new game but no, it still persists.

Any idea of cause and/or fix?