4.0 missfire

A mid range RPM miss is hard to diagnose as it can be one of several things. Most likely is ignition as your tech zeroed in on, but this includes plugs, plug wires, distributor, rotor, and coil as well as the electronics that tell them when to fire. Begin with a simple tune-up and go from there if the problem persists.

That has been done,cap-rotor-plugs-wires.

What kind of plugs? And give us a full description of what has been done please, don't make us pull it out of you one step at a time.

I am guessing you have done the simple things such as plugs,wires,cap and rotor. My next guess would be to check the...
. distributor for play
. check grounds
. check cps and hall sensor

pete