As for fully unlocking it i'm not familiar with your system so I'm sorry I can't really help with that, but if that is in fact the problem I'd search around for how to unlock it or maybe even get a laptop cooling pad
It is very likely that it has gone bad. The card it probably underclocking itself due to the heat and cause those sudden moments of fps drop then it goes back to the default you have when it drops back down in temp and back and fourth.