I have been looking into getting an exhaust and intake system on a 2001 ranger with a 4.0L 4x4 and was wondering if it made much of a difference in performance and fuel milage? and what type of system to put in it? I have been told k&N intake and a single vortec exhaust.

 

You'll notice more power at higher engine speeds. And it will be a little louder and meaner sounding If you can keep your foot out of the pedal, your mileage should be a little better, since the engine will breathe better.
Most people recommend Gibson for performance exhaust, and flowmaster for sound.

 

Actually...along with the performance gain, I've noticed that I get better gas mileage now when I have my foot harder on the pedal. When I just cruise I get 20-21 MPG. When I'm rompin around I get 23-25MPG. That might be a feature specific to just 4 bangers though.
As far as intake and exhaust...my only recommendation is that you do them both at the same time because one has little effect without the other.