2002 transmission grabs briefly at stop.
 

Hello,
I have a 2002 V-6 Explorer XLT with 103K miles that recently has started developing a problem. Sometimes when I am completely stopped, engine idling, and in gear in drive, the transmission seems to grab momentarily. During this brief event the engine rpm's reduce slightly and the transmission seems to engage a little so it feels like the car wants to move forward. During this event the engine does not die but it's troubling me. This event does not happen every day when I drive this car, but it seems that it happens more often on colder days and during the first 15 minutes after starting out. Any help or insight would be appreciated. The automatic transmission other than this problem operates great.
Thanks, Matt