My truck started this weird vibration a few weeks back. It only does it over 64-65mph and it is not engine rpm related only mph. I took it to the dealer and they said the drive shaft was bad. i know they are just throwing parts at it. So i picked it up toady and as i expected it still does it. Its very rythmic. It goes vib vib vib nothing vib vib vib nothing. It gets worse when you tow or put weight in it. anyone have this problem and a fix so i can tell them where to look. thanks kenny