What are signs that my ford expedition needs a tuneup?

My sister has a 1997 ford expedition xlt and i was wondering what are some sign for this specific suv that it needs a tuneup? Some of the sign i see is when you are driving it the engine sounds different than it use to sound ( know it sounds more like a tracter engine and before it sounded like a 5.4 L triten engine) and one thing it has dual rear exit exhaust. And one more thing i noticed is that when you first takes off it shakes real bad.What are signs that my ford expedition needs a tuneup?it will run like s*** no power no good gas miles