I just bought truck. Only has 63000 miles. After driving for a few days I started feeling a vibration. At first I thought I was running over rough spots in pavement like the warning marks on the shoulder. It starting doing it more frequent so I began taking notice of when it was doing it. Every time it does it it is changing into overdrive.It last about three seconds and it doesn't do it every time it goes into overdrive. There does not seem to be a pattern. No noise or vibration in other gears. Would appreciate any thoughts. Thanks.