Steve, I have a 98 Ranger XLT 4WD 3.0 manual five speed. I am reading 92k on my odometer and I just started having the exact same problems you have had. I changed my plugs two weeks ago and that seemed to help. They definitely needed to be replaced. I also ran injector cleaner. The problem seemed to go away, but a few days ago, it came back. Hesistation when taking off, low idle hesitation, sustained speed (on highway) bucking... The only thing I haven't done yet is replace my wires which I intend to do very soon. The funny thing about it is, my gas mileage is better than I have ever had. (20+) I can't complain about that, but it definitely is running very rough.
When you get yours back, let me know if changing the wires took care of it, would you?