For op, I have the same issue you do. When you describe the vibration you experience I know exactly what you're talking about. Except I have a 4x4. The vibration starts around 65 for me. It then gets progressively worse as I speed up. The faster you go the worse it gets. Unlike tire issues which tend to improve once you get to 75 +, this vibration keeps getting worse. I have literally gone through FOUR sets of tires, and FOUR sets of wheels, all of which have been road force balanced together. And the high speed vibration has never gone away, so I am 100% positive it has nothing to do with tire/wheel balance. Driving on the highway is intolerable. I literally hate it and avoid the interstate at all cost
And you can tell a tire vibration by how it feels and sounds. My steering wheel feels tight, no vibration. Rather this vibration comes up somewhere through the chassis and vibrates the whole truck at a higher frequency. You feel it in the seats and can even see them vibrating. You feel it in the floor boards and it feels like the truck is almost vibrating side to side slightly right? Vibration is not dependent on engine rpms for me, but strictly speed. Which tells me it must be a spinning part in the drive line. Does this describe your vibration op?
I have also replaced my entire front end, so I know this is not a balance or suspension issue. I am suspicious of
- rear drive shaft still
- rear pinion
- rear wheel bearings
- transmission mount
- rear main
- and now the torque converter, as was mentioned earlier
I also replaced my rear u joint with oem recently, as I found the old one had a tiny bit of slop. But it made no change. At this point I don't know how to figure this out, so I'm probably going to bite the bullet and take it to my local toyota dealer, and tell them I don't want the truck back until they have found the source of this stupid vibration. That may be your best option op, because I have literally been replacing parts trying to figure this out for YEARS now