So I did the TJ coil add-in, netting a tad under 2" on my back end. Only other suspension mods are ~1" longer shackles. '89 4Runner.
Now, at high speeds (> ~55 mph), I'm getting a grinding/sliding noise that seems to be coming from ssomwhere in the driveline. Only occurs right at the transition point as throttle is applied, or being let off - like only the slightest torque applied will do it. Sounds almost like the TC output shaft is sliding in the driveshaft or something....?
What bugs me is, after so liffle lift? I know 2 things have changed, pinion angle and TC-to-pinion distance... but I can't figure how either of these would cause such an effect?
As mentioned, only audible at higher speeds and at that transition point... gets louder as speed gets higher....?

might be the driveline is to short.don't have to be that much to short to cause problems at higher speeds.just my .02

Longer shackles changed the pinion angle:
- http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml#Single-Cardan-Measurements

But try pulling the shaft apart and brush some grease on the slip yoke splines. It may have pulled apart a bit and might be dried out there. Also, check the u-joints for play or tightness.

Hm, no play that I can detect w/ in in place... I greased the snot out of both of 'em. i'll try pulling the shaft though and have a look at the inside.

One problem with greasing the slip yoke is look at where the grease goes. It usually ends up inside the shaft, not on the splines. Over time, the grease will usually work it's way down to the splines but that takes some compression/extension cycles to do that.

I pulled the shaft off for a good sinpection... no obvious problems. The slip yoke does have some black scarring on the surface up at top by the u-joint, but it's stil smooth and feels fine once cleaned. I can only asume this is from a combo of exposure and grese ground in.
Cleaned and lubed the yoke and splines, made sure there was lot of grease in/around the DS everywhere. Also checked both u-joints, by hand they "feel" smooth rolling around, and have plenty of greae 9at least when I aply the gun, grease comes back out the fitting0
Unfortunately, the problem persists. It is a little quieter now, but not by much.
I do wonder if possibly the upper u-joint has a bad bearing or something in it, and it appears only at high revolutions and when only very slight torque applied (no noise heard with any throttle).
Is there any way to tell, w/o jut replacing it? i rottated it around by hand and didn't feeling any sticking or aything.
Note also the angle is pretty minor, total lift only about 2.5".

Do you have grease coming out of the bearing caps on the cross? That is where you want it coming out, not the fitting. Take the zerk off the joint, stick it on the grease gun and pump it to make sure grease coming out the end, sometimes they get clogged with hard grease/dirt.

It may just be a small lift but the angles have changed on the d-shaft and it may be enough to cause problems

Finally got some free time to get back to this.
I pulled the D/S off again, and cleaned out both U-joint fittings, repacked w/ grease. Did get it coming out the bearing caps on the ends. old stuff was black and thin, new now nice and thick/blueish (synthetic).
Unfortunately, the noise remains. It's not quite as loud, but definitely still there.
With the new grease, the U-joints flop around quite easily, gravity alone will pull them around. On one I *think* I can detect a very small side/side motion but *if* it's there it's subtle. I am kind of out of ideas as to what could be doing this - am I stuck w/ just replacing both joints/ I'm sure they're original.
Just one other thing... any idea just how much grease should be on the inside of the slip yoke/driveshaft? There's a fitting up at the top... when I had it out, I made sure there wass some in it, and greased the ouside of the yoke... looks like you could fit a nearly a whole can inside of there, but I don't see what good that would do you?

I only put about the same amount of grease that the u-joints take into the slip yoke. Too much in there is not good, it can cause the slip yoke to not compress all the way w/o squeezing out the excess grease. If you bottom out hard, that can cause the t-case output to get damaged with the shaft pushing into it too hard.

So I took the DS w/ joints attached to a local DS shop. He saysd the joints looked great to him. After discussion, didn't really think the problem was DS/joint related, what about the output flange on the TC.
Well, I did notice last night that I can wggle that flange a bit. Very slight, but there; more than the pinion end on my newly rebuilt 3rd for sure. This evening I'll see if I can mic the movement.
What's involved in tightening that thing?