Odd vibration

[07EddyB]

So for a few months now I've had a vibration in the Explorer (2007 127K). I don't have any OEM bearings anymore - they've all been replaced at least once. And it doesn't feel like a bearing. With bad bearings it's usually more pronounced at a certain speed and there is usually some noise.
I call it a vibration but it's more like a shudder. You know when you drive around with the windows down on a windy day you get that rough, shudder feeling when the wind blows in just right? That's what it feels like. In fact, I dismissed it as that since I rarely use the AC - but one day I did and it was still there.
It doesn't seem to start until about 45 and it really doesn't get any worse with speed. I don't really feel it through the steering wheel - it's like the whole body just shudders. And it's not continuous - it happens almost constantly but not in a pattern if you know what I mean. I've put it in neutral running down the road and it doesn't help so the engine is out and likely the transmission as well. Applying the brakes doesn't help. Last weekend I rotated the tires (which had been done just 6K miles previously) to no effect. If it was an out of balance tire I would think that it would get worse with speed. I've gone through the front and rear suspension as well as I know how to and nothing is loose.
In a way it feels like you are running on a less than smooth road but everything is being amplified into the frame more so than usual.
I know it's a long shot - but has anyone else run into this before? It's frustrating because it doesn't seem like the standard methods to diagnose it are working. If you want a little taste of what it feels like (close but not exact) then go down the road with your front windows up and your rear windows down. The buffeting that will ensue is pretty close to what I'm feeling.

 

[rustylugnut]

A common problem with these trucks is torque converter shudder around 35-50mph. It is often described as feeling like driving over a rumble strip.

 

[07EddyB]

So it's been two months or so - I drove out to a friends house a few weekends ago and I was on a road that had several new paved sections. I noticed that the vibration all but went away on the new pavement and came back on the old pavement. The Ex has been feeling pretty sloppy lately so I decided to take a chance on the struts. I understand that worn struts aren't supposed to be a vibration issue - but maybe they are causing the road imperfections to be amplified. So last weekend I put new KYB quick struts on the front - this morning I put new KYB quick struts on the rear. The fronts helped but didn't really solve the problem and I've only driven a few miles now on the rears but the truck is tight with all four replaced - it doesn't have that sloppy feeling anymore. It feels noticeably better - I don't regret the new struts at all.
Waiting for everything to settle in and see where I'm at but I'm hopeful this will settle things down. I'll report back in a few weeks after everything has worn in.
For the record - it's a 2007 with 129K miles.