This is a classic symptom of not enough processing power. I am guessing that your songs have become more complex since you first started using your new set-up. Try lowering the sample block size (Preferences/Audio Device) - note that this doesn't effect your sample rate. Unfortunately if that doesn't help then you are probably looking at upgrading you system. I note that Presonus state that an i3 processor is the minumum system requirement to run Studio One, but if you search the knowledge base they say that they recomend an i7 4 core, with a native speed of at least 3Ghz. That's a lot more than their stated minimum... I'm sure it's no concilation, but I've been in exactly the same situation. All the best,
M