This program completely erase any leftover of old drivers.
http://www.guru3d.com/files-details/display-driver-uninstaller-download.htmlDownload the latest version, then it should appear in your download folder, go into the download folder and extract the DDU archive into your download folder, 3 new things should appear in your download folder. Go to GeForce.com and download the latest nvidia drivers. Then look for a white and grey icon that says DDU in the download folder and double click on that. It will ask you to go into safe mde, say yes, it will restart the PC and bring you to safe mode, then a window should pop up to ask you what drivers to uninstall and clean, double click on the DDU icon again in the download folder if it doesn't pop up . Then choose nvidia drivers to uinstall. Now choose clean and restart as it recommends to you, then just let it do the work and then it will restart and bring you back to desktop. After that, just install the nvidia drivers you downloaded in your download folder, after its done, restart one more time just to be sure everything is running as intended. I'm sorry I can't be more specific, since I'm not at home and on my PC atm, I hope it's clear enough to understand though.
After all that is done, try other games that is equally demanding to PvZ GW2 to see if you face the same heat problem. If you still do, then I think it's a hardware problem, which you can try to send it back for warranty repair if you're still under warranty or buy a new GPU. There's not a lot you can do about heat problems other than clean the GPU, raise the fan speed to higher setting which gets louder, or go with water cooling. Obviously water cooling is expensive, so that's not exactly an option to consider.