on my 89 i put an intake, some headers,a high flow exhaust i also removed the clutch fan and replaced it with some electric ones and that made a huge difference. im happy with the way it runs but wouldnt mind getting more power out of it.

 

From what I have read the 4.0 is pretty torqued out of the box. Of course a free flowing exhaust and a decent intake setup (K&N) will make a nice difference.
When deciding a cam you must consider all aspects of the motor and its use, The cam selection will not add power to an engine !!!! It will however allow you to "Focus" the HP and Torque curves to match the intended use. Many people tend to think that a Cam is a mjic Bullet for HP's but it isn't. The cam Timing is much more important than having tons of lift also...Just for what its worth!

 

Thanks for the advice