Was working fine, now getting unplayable FPS

[GoldPlatedCig]

Got the game working beautifully. Installed a few compatible mods, but was getting low fps. So then started deactivating one by one in order to figure out which mod could be causing it. Ended up deactivating all of them, still was getting low FPS. Looked in the ini 's to make sure nothing was changed, it was all in order. Any idea what could be happening?