Hmm, it may be a problem with the game or an incompatibility between the new nvidia drivers and the Borderlands 2 which is older. The fact that GTX980M is quite new in both arhitecture and on the market may cause some troubles with older games.
Try changing the settings in your Nvidia Control Panel--> Manage 3d Settings ---> Choose Borderlands 2 ---> Put Power Management on Full Performance (or whatever it says) . And you should also go to the Physx settings in Nvidia control panel and select your GPU for Phyx because the game may change between CPU and GPU to process physx.
Try these out and see if something changes.