I put in the Coastal 80W90, which contains no LSD friction modifier additive. I didn't add any modifier of my own initially, and since I'm having no problem with the diff "chattering" I think I'll keep it that way.

Immediately after changing the oil, I did a couple of "tests" in my parking lot. I backed both rear tires against the 5" tall square-top curb and tried to ease up onto it. It's just enough to keep me from making it without any inertia. Just as the tires started to climb and the contact patch left the pavement, both rear tires started to spin and my rear end started inching to the left down the slight slope of the lot. Hmm, so far so good.
On Saturday I went to an industrial park and did the old "RTI" thing on a loading ramp in 2WD. As soon as one of the rear tires left the ground, it just spun and the other side really didn't push at all. Probably asking too much from that one.
Today in the rain I would break the tires loose when pulling away from intersections/lights and it felt like I was getting more traction than if one tire were spinning, always got a decent push.
Just got back from lunch and I went behind a vacant strip mall to the loading area and did a few peel-outs. I consistently laid down two marks on the gritty/sandy pavement. That's the best test yet.

Brent