transmission moves in and out of overdrive
 

98 civic lx- auto trans, tuned and has fluid. Has anyone had a problem with the trans. slipping out of overdrive. It happens most often at freeway speeds. You can see the tach jumping 2500 to 3000.The other gears seem to shift ok. I was hoping it may be a sensor or something I could try before I take it to the $transmission shop$. thx.