I'm running Theme Hospital on my MacBook Pro. It has all the necessary requirements to run the game as it has been playing extremely smoothly for months. This all changed when I upgraded my MacBooks HDD to a 960GB SDD and also upgraded the RAM to the maximum capacity of 8GB. Obviously I cloned my drive and every single application runs effortlessly on my new SSD. I opened up Theme Hospital and was surprised to see that everything looked 'smooth', even the font that shows at the beginning when you run a program.
The game is unplayable now and is incredibly jerky and slow. I just want to know what has changed and how it can be fixed. I've already uninstalled and re-installed and still get the same problem.
Can someone please help?!?

Sounds like one of the stupid scaler's got switched on. They also require more CPU if used. You could try launching the game with alt-double-click and seeing if there is a spot to change that. Worst case you can back up your saved games and choose Reset game data. You can actually fix this by just editing the correct file and changing the scaler to normal2x/normal3x, but I don't recall which one it is.