serging speedometer and tachometer

My 1999 Plymouth grand voyager SE 3.3liter engine has developed a tach and spee
dometer problem.At various times the tach will surge@ 200 rpm and at the same time the speedometer will top out and then they will return to where they should be.I can make this happen also bye driving in reverse,stopping and putting it in overdrive and the tach and speedometer will serge without the car ever moving.Anyone have an idea or know what's going on. I don't and could use some help.Thanks to all with an imput.Charlie

First make sure your battery and connections are up to the task. These vans are sensitive to low erratic power. Second, try a cluster self test. Hold the trip and reset knobs in then turn the key to "on/run". After a few seconds the instruments and lights will start to cycle on their own. The speedo and tach will cycle to 4 readings then return to zero.

Rip,Charlie here. Got your maybe fix that seems to have turned into a fix.Don't know yet,haven't taken it for a long test drive yet but the backup test proved to be a no problem here thing.Thanks a bunch Rip.:licka: