Hum.. I'm just not sure about a 2000 ranger. But I know that most modern cars have a processor in the guage cluster to buffer these types of readings.
They do the same thing with your speedometer, tachometer, oil, and temp guages. They are all buffered by a software engineer and marketting weenies who think the end consumer will be confused by guages that move in real time. Given my experiences with the average car operator... they are probably correct.
If it really bothers you.. I'd say it's one of two things. Either a loose / grounding wire or a bad guage cluster.