The code reader is the best route.

If the maintenance is upto date (plugs,  filters and wires) check the
MAP sensor.
The  problem on my '94  4.0L turned out to be a white powedery deposit
on my MAP sensor.  I used contact cleaner to remove the deposits.  The
truck ran like a top.  Engine light went out. MPG increased and no
more surging.
Be very careful with the sensor.  DO NOT use a brush or even touch the
fine wires on the sensor.

Pull codes and tell us which ones come up.

If you look along the bottom of the dashboard, in the vicinity of where your
left leg rests while driving, or perhaps just to the right of the steering
column -- different vehicles move the location around, but all have it along
the bottom of the dash -- you will find a data port connector that is
clearly identified as a test port.

Go to AutoZone, they will either connect the scan tool and pull codes for
you, or give you the scan tool to use in the parking lot to pull the codes
yourself. If you want to drive a different car to AutoZone, they will sell
you the scan tool, and you take it home. When you are finished, you bring
the tool back for a full refund, making the use of the tool free.

The tool simply plugs into the data port, and you follow the directions.
Reset the codes and fix the trouble. AutoZone hopes you buy the repair parts
from them, this is why the let you use the tool for free.

Given the description of your problem, I expect you will find some sort of
misfire -- broken plug wire, bad plug, something like that. But, DO NOT pick
up any wrenches based on that guess, pull codes and fix what the truck is
asking you to fix.

I like this site to diagnose the codes ...
http://autorepair.about.com/od/obdcodedatabase/a/OBD_1996_year.htm

I have a 97 Ranger XLT 4x4, 4.0 6 cylinder with 118k miles.  The
engine has been running rough and often "bucks" while driving.  The
check engine light is on full time.  Any ideas what might be wrong?