1991 Pick-up V6 Automatic
 

I have a 1991 pu and the transmission indicator lights in the dash panel while driving goes off (D) and sometimes it feels like it comes out of overdrive. You can just bearly touch the gear shift and the light comes back on and then back into overdrive. I've tried to move the gear shifter back and forth while driving but I cannot duplicate the problem. It happens about every 4th or 5th time driving it. Any help would be appreciated.
Thanks, Ray