@Kyle > Three things for you to try:
1) Go into your System Preferences and at the top where it says "Automatic Graphics Switching," un-check that.
Try again -- if you still have problems...
2) Open the rekordbox Preferences and on the View page, change the waveform drawing rate from High to Medium.
If that's STILL a problem...
3) Go back into the rekordbox Preferences and set the audio buffer to a value double what it's currently at.
If things persist in being laggy, please open your Activity Monitor and take a screen shot of the CPU, Memory and Energy pages please.