97 dodge dakota

i have codes that are all dealing with misfiring on 1-3-5.  i did a tuneup on it.  i light goes out, i drive it for a couple of days the light comes back on reading misfiring on a different cylinder.  it is always on that side of the cylinders.  It came on again today it reads misfiring on cylinder 3.  I have done tuneup after tuneup, change sensors, changed fuel injectors, can any one please help me.