So I just bought a 2000 Ex a couple of weeks ago. 200K miles,4x4, 4'' lift(front leafs say Rancho on them so I believe its a Rancho lift), 315/75r16 tires on stock wheels....I've already rotated/balanced found 1 slightly bent wheel. Tires all balanced good....starting @ about 50mph you can start to feel it, about 65mph it gets the worst and smooths out again until you hit about 75...then it gets worse until about 80 then smooths out. 80 and above you don't feel it so much, but you can tell it's there and still "hear" it. To me, it feels exactly like ujoints but I've already replaced them with no change at all. The vibration is throttle sensitive. As soon as you let out of throttle, it goes completely away. I don't have any special tools available to me to detect vibrations like a dealer would have...but one thing I noticed, my old F250 had I'm pretty sure the same driveshaft, and the slipyoke on the 250 was more towards the rear(driveshaft has flanges on both sides..). I could be mistaken about that though, but somehow could the driveshaft being backwards cause a vibe like this? I'm 99% sure the yokes are phased correctly because it looks like the ujoints I replaced were stock and never removed. I would figure though if it were a driveshaft balance issue the vibration would be constant and wouldn't go away when out of the throttle. FWIW....I'm pretty sure the previous owners were chasing this vibration as I bought it with the front driveshaft missing. All fluid levels/conditions checked out good and I couldn't feel any looseness in any bearings anywhere. Any good suggestions??