hey guys got an 02 ext cab shorty. 260km on it. when i hit overdrive a have a small vibration/ hummm.......hummmm at low rpms, when i get up in rpms it goes away. no vibrations if let off the throttle. in 4x4 it sounds worse. i had same issue last year and replaced tranny mount,fixed issue then, mount seems ok now. i blew out the bearing in front drive-shaft in the summer, pulled it and drove around all summer without it and no vibs. had driveshaft rebuild and re-balanced and now this vibration. any help much appreciated. tc shifts smooth in and out.

 

sounds like driveshaft is not balanced properly if changing that caused a vibration...