Been trying to pin point this issue for awhile, kinda got it narrowed down by replacing some beat, worn out parts. Still haven't solved it. I own a 1996 Dodge Ram 2500, light duty 4x4. Happens between 66 and 68 MPH. It was worse before replacing the drum's. Had the tires balance twice. For some odd reason, I feel the kid that installed my tires did a half ass job. I got a very slightly bent wheel but was told that wouldn't be the issue. Several months ago I found out I have been running the transfer case dry. FYI, if you buy a highly used truck. Check all the fluids. Anyway, I don't think that could be the issue. Any input is welcome, its ****ing annoying having to deal with it.