Try Nouveau, like Brickfrog said, if only to test the gpu.

I dont know if its the same but in Mint the Synaptic Package manager shows me all the versions of the nvidia driver supported by the kernel. Maybe you can downgrade your driver with it, although, I dont know how would you do that. Im just guessing but I think you would need to switch the transitional packages and those pull all the packages related to the driver.

Also, I’ve read a few times that distro upgrades can have weird problems and clean installs are better.