Well we changed the fluids Wednesday night and there seemed to be an improvement during straight-line driving, but during turns the violent thrutching was still present unless I threw it into Neutral and coasted through the turns. Friday night while driving home, I lost drive and started hearing some ominous noises in the rear end. I pulled over, popped it into 4-LO and drove home in Limp Mode (FWD only?). A look underneath today revealed that in 4-HI the rear drive shaft is turning but the rear wheels aren't (but they 'try' a little)! Thinking the worst, I suspect the rear diff/ELSD is gone, however I am searching for alternatives so I don't bark up the wrong tree and waste a lot of $$$ and effort tearing the rear end apart. My question is, is the 'default' (i.e. unpowered) ELSD mode unlocked where there is no torque to either rear wheel? I disconnected the FDCM to reset it, then plugged it in again (no difference in behavior with it unplugged). I am now getting a U0114 code (no comm with FDCM) but I expect that to clear after a few (more) starts.