I came to a stop light on the rood. I put N & waited a min. When i tried to move forward by moving the lever to D. The lever didn't move as it is locked. I didn't force it but tried to push the button on the lever while moving the lever to D, but it didn't move, suddenly,succeeded to move it to D smoothly. I continued to home normally. tried to move to N THEN TO D again in the garage, the lever acts normal. Noting that nothing on the dash showed an error. What could it be?

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X5 3.0i SUV
2005 -113000 miles
GM-A5S 690R Tranny