What and why is my jeep skipping?

Okay so I drive a 2006 jeep liberty and for almost about a year now every once in a blue moon it feels like it's skipping or kinda sluggish, but recently it seems to happen more often! I'm not sure if it's had a tube up or anything done to it when I got it but I know I haven't done anything to it and I've had it for two or three years besides for oil changes and it's at 78000 miles! What could it be???