Twisted Treeline FPS issue.

I hope this is the right place to put this. Anyway, for some reason, I get half or lower FPS in Treeline vs Summoner's Rift. It wasn't like this before so I don't know what could have triggered it. Before you say update drivers, my drivers are up to date. This issue has been going on for maybe 2-3 months now.

Is anyone else having this issue? It's not unplayable, but it does have a significant impact on game play.