I believe I've discovered the source of the issue; the Neptastic mod. I deleted it and started the game up again and it runs at solid 60fps in Performance Mode. I don't know why Neptastic made the game run so poorly when it was recommended to me to boost performance and prevent crashes. Did I have the settings configured wrong? Or does it have compatibility issues with the Ally or AMD in general? It has a setting for VSync in it, which is an NVIDIA setting, which tells me it's made with NVIDIA cards in mind.