At this point, I'm pretty sure I'm not dealing with wheel bearings, half-shafts, or transmission bearings (I've replaced some/all of these components). I'm down to the idea that it's bushings or transmission. It did happen suddenly, so it seems odd that it would be a bushing issue. I wouldn't want to take the car up faster than 25MPH. No rubbing sounds, no issues/changes under braking.

Nothing while coasting, but the car jitters and shakes under acceleration. Engaging 4WD doesn't seem to change anything.

Car does have an SJR lift and 6 lug wheels. Car has been fine for years with this setup, but started having issues earlier this year.

Current trans is a 3 speed auto, but I have a 5 speed manual that I picked up to eventually swap. Has anyone had a similar issue?

Vibration under load, accelerant or uphill, is almost always the inner CV axle joints or the front diff. Since they’re almost touching it can be hard to distinguish the two. 

with the lift my guess is the axles. I have an SJR 2” lift and aftermarket axles can’t handle it. Bang bang bang rear view mirror shaking 

Edited January 5, 20242 yr by idosubaru

It could be a damaged outer CV joint. I had an issue with my brumby where there was a very bad shimmy at speed that would slow down with the vehicle speed to the point that the steering wheel would wobble left and right with the tyre rotation and it was speed sensitive. 

The issue turned out to be an outer CV joint on the left hand side that would lock up at one point through its rotation with the stub axle on an angle. It was extreme and I could replicate it with the CV shaft in my hands. Yours may be more subtle than this though. 

I’d start by swapping out the shaft on the side you feel that the shimmy is induced from then the other one if it the shimmy is still there. 

Cheers 

Bennie

I've had the same symptom on my wagon.  Ended up being the inner CV joint on one of the front drive axles (I forget which side).  Exactly as IdoSubaru described.

My 2 bucks

How about ball joints?